Angels have a special commission to guard believers

Psalm 91:11, 12  For he will command his angels concerning you to guard you in all your ways; they will lift you up in their hands, so that you will not strike your foot against a stone.

These are the verses that Satan tried to misuse when he tempted Jesus in the wilderness. We are not to tempt God but we are to be confident that his angels will guard us in all our ways, if we are believers. They will make sure we come to no harm.

Spurgeon says that rather than having "one guardian angel, as some fondly dream" all the angels are active on our behalf. He calls them "the bodyguard of the princes of the blood imperial of heaven".

"It is down in the marching orders of the hosts of heaven that they take special note of the people who dwell in God. It is not to be wondered at that the servants are bidden to be careful of the comfort of their Master's guests; and we may be quite sure that when they are specially charged by the Lord himself they will carefully discharge the duty imposed upon them."

"The protection here promised is exceeding broad as to place, for it refers to all our ways, and what do we wish for more? How angels thus keep us we cannot tell. Whether they repel demons, counteract spiritual plots, or even ward off the subtler physical forces of disease, we do not know. Perhaps we shall one day stand amazed at the multiplied services which the unseen bands have rendered to us."

"as nurses carry little children, with careful love, so shall those glorious spirits upbear each individual believer ... even minor ills they ward off. It is most desirable that we should not stumble, but as the way is rough, it is most gracious on the Lord's part to send his servants to bear us up above the loose pebbles. If we cannot have the way smoothed it answers every purpose if we have angels to bear us up in their hands. Since the greatest ills may arise out of little accidents, it shews the wisdom of the Lord that from the smaller evils we are protected."

Angels praise God

Psalm 103:20-21 Praise the LORD, you his angels, you mighty ones who do his bidding, who obey his word. Praise the LORD, all his heavenly hosts, you his servants who do his will.

(See also Psalm 148:2 Praise him, all his angels; praise him, all his heavenly hosts.)

Angels have good reason to praise God - For their creation by God, for their preservation, for their happiness, in which they continue as they are elect of God in Christ.

They are always employed in the work of praising the Lord nor are they in the least backward in it, nor remiss. That is not why they are addressed as they are. Rather the design of the psalmist is only to show how great and good the Lord is and that angels, as great as they are, are under an obligation to praise him, and are bound to do so. He also intends to stir himself and others to this work, from such a consideration - that such noble creatures praise God.

C H Spurgeon

Finding his work of praise growing upon his hands, he calls upon "the firstborn sons of light" to speak the praises of the Lord, as well they may, for as Milton says, they best can tell. Dwelling nearer to that prepared throne than we as yet have leave to climb, they see in nearer vision the glory which we would adore. To them is given an exceeding might of intellect, and voice, and force which they delight to use in sacred services for him; let them now turn all their strength into that solemn song which we would send up to the third heaven. To him who gave angelic strength let all angelic strength be given. They are his angels, and therefore they are not loath to ring out his praises.

Angels are referred to together as a heavenly host

Psalm 103:20, 21 Praise the LORD, you his angels, you mighty ones who do his bidding, who obey his word. Praise the LORD, all his heavenly hosts, you his servants who do his will.

Psalm 148:2  Praise him, all his angels; praise him, all his heavenly hosts.

The idea of hosts is also attached to armies and to stars. The angels form a great army, an army of light. (Cf Job 38:7; Revelation 9:1, 11).

Angels are on rare occasions referred to as gods

Psalm 8:5 You have made them a little lower than the angels (gods) and crowned them with glory and honour. 

Psalm 97:7 All who worship images are put to shame, those who boast in idols -  worship him, all you gods!

See

Hebrews 2:7 You made them a little lower than the angels; you crowned them with glory and honour

Hebrews 1:6 And again, when God brings his firstborn into the world, he says, "Let all God's angels worship him."

2:7 Angels are mighty ones, gods of a sort. 

Angels are sometimes referred to as Sons of God

Job 1:6 One day the angels came to present themselves before the LORD, and Satan also came with them.

Job 2:1 On another day the angels came to present themselves before the LORD, and Satan also came with them to present himself before him.

Job 38:6, 7 On what were its footings set, or who laid its cornerstone - while the morning stars sang together and all the angels shouted for joy?

(Psalm 89:6 For who in the skies above can compare with the LORD? Who is like the LORD among the heavenly beings? [Sons of God])

Not only Christ an his people but angels, because they are so close to God, are known in the Bible as sons of God.

Angels always obey God

Psalm 103:20, 21 Praise the LORD, you his angels, you mighty ones who do his bidding, who obey his word. Praise the LORD, all his heavenly hosts, you his servants who do his will.

Instinctively and immediately angels always obey God's commands. This is the main basis for the part of the Lord's prayer wherewe are to ask that God's will be done on earth as in heaven.

Angels are capable of swift flight

Daniel 9:21 ... while I was still in prayer, Gabriel, the man I had seen in the earlier vision, came to me in swift flight about the time of the evening sacrifice.

Swift flight is no doubt a metaphor of some sort, a theriomorph of some description. What it identifies is the ability of Gabriel and other angels, no doubt, to travel speedily. Without the aid of machines or other helps of that sort they are able to cover huge distances in a short time.
This would seem to fit in with
Revelation 14:6 Then I saw another angel flying in midair, and he had the eternal gospel to proclaim to those who live on the earth - to every nation, tribe, language and people. 

Also Psalm 104:4 (quoted in Hebrews 1:14) He makes winds his messengers, flames of fire his servants.

Angels are involved in miracles, live in heaven and have a measure of greatness

Psalm 78:25 Human beings ate the bread of angels;* he sent them all the food they could eat.

We know that there was something supernatural about the manna that the Children of Israel ate in the wilderness. It fell daily from heaven just where the people were. It had variable properties that made it rot if kept overnight except on the night before the Sabbath. Asaph here calls it the bread of angels. Now why does he call it that? Certainly, angels are spiritual beings and have no need of food. The Puritan Arthur Jackson makes three suggestions as to what Asaph may have in mind

1. Because it was provided and sent by the ministry of angels
2. Because it seemed to come down from heaven, the dwelling place of the angels
3. To set forth the excellency of this bread, that it was meat, as one would say, fit for angels, if angels needed meat.

Coming at the matter from the other end then, we remind ourselves that God delights to do his miracles through the agency of angels and that heaven is their home, there in the presence of God. They are also a useful benchmark for excellence or greatness.

* The Hebrew has mighty ones but the LXX legitimately has angels

Angels were involved in the giving of the law

Acts 7:53 you who have received the law that was given through angels but have not obeyed it.

Galatians 3:19 Why, then, was the law given at all? It was added because of transgressions until the Seed to whom the promise referred had come. The law was given through angels and entrusted to a mediator.

Hebrews 2:2 For since the message spoken through angels was binding, and every violation and disobedience received its just punishment, ...

Deuteronomy 33:2 He said: "The LORD came from Sinai and dawned over them from Seir; he shone forth from Mount Paran. He came with myriads of holy ones from the south, from his mountain slopes.
Psalm 68:17 The chariots of God are tens of thousands and thousands of thousands; the Lord has come from Sinai into his sanctuary.

Matthew Henry comments on Acts 7:53 that the law is said to be received by the disposition of angels, because angels were employed in the solemnity of giving the law, in the thunderings and lightnings, and the sound of the trumpet. It is said to be ordained by angels (Gal. 3:19 ), God is said to come with ten thousand of his saints to give the law (Deu. 33:2 ), and it was a word spoken by angels, Heb. 2:2 . This put an honour both upon the law and the Lawgiver, and should increase our veneration for both. But those that thus received the law yet kept it not, but by making the golden calf broke it immediately in a capital instance.

Barnes notes that the phrase given through angels has been supposed to mean that the Law was given “amidst” the various ranks of angels, being present to witness its promulgation. Others suppose that the angels were employed as agents or instruments to communicate the Law. All that the expression fairly implies is that the Law was given amidst the attending ranks of angels, as if they were summoned to witness the pomp and ceremony of giving “law” to an entire people, and through them to an entire world. It should be added, moreover, that the Jews applied the word “angels” to any messengers of God; to fire, and tempest, and wind, etc. And all that Stephen means here may be to express the common Jewish opinion that God was attended on this occasion by the heavenly hosts, and by the symbols of his presence, fire, and smoke, and tempest.