Note: All Scripture quotations found in this article are from the text of the Authorized King James Version of the Bible.
Angels are divinely created beings that were here before anything material. (Colossians 1:16)
Job 38:4 "Where wast thou when I laid the foundations of the earth? declare, if thou hast understanding. 5 Who hath laid the measures thereof, if thou knowest? or who hath stretched the line upon it? 6 Whereupon are the foundations thereof fastened? or who laid the corner stone thereof; 7 When the morning stars sang together, and all the sons of God shouted for joy?"
They were created for God's glory.
Revelation 5:11 "And I beheld, and I heard the voice of many angels round about the throne and the beasts and the elders: and the number of them was ten thousand times ten thousand, and thousands of thousands; 12 Saying with a loud voice, Worthy is the Lamb that was slain to receive power, and riches, and wisdom, and strength, and honour, and glory, and blessing. 13 And every creature which is in heaven, and on the earth, and under the earth, and such as are in the sea, and all that are in them, heard I saying, Blessing, and honour, and glory, and power, be unto him that sitteth upon the throne, and unto the Lamb for ever and ever."
Angels cannot marry, nor reproduce like humans. That being said, all angels are an individual creation of God.
Matthew 22:30 "For in the resurrection they neither marry, nor are given in marriage, but are as the angels of God in heaven."
In scripture there are never any female angels. They are always said to appear as men without wings.
Genesis 18:2 "And he lift up his eyes and looked, and, lo, three men stood by him: and when he saw them, he ran to meet them from the tent door, and bowed himself toward the ground,"
(Also read Genesis 19:1-12)
Although angels cannot reproduce, the fallen angels(sons of God) that left their first estate were able to reproduce with the daughters of men. The fallen angels that rebelled with Satan will end up in the lake of fire.
Genesis 6:2 "That the sons of God saw the daughters of men that they were fair; and they took them wives of all which they chose."
Matthew 25:41 "Then shall he say also unto them on the left hand, Depart from me, ye cursed, into everlasting fire, prepared for the devil and his angels:"
The only time that spirits appear as female, they are not angels, rather devils with wings of a stork. (Zechariah 5:1-11)
Angels announced the birth of Jesus Christ(Luke 2:10-14), witnessed his incarnation and rejoice when men get saved.
1 Timothy 3:16 "And without controversy great is the mystery of godliness: God was manifest in the flesh, justified in the Spirit, seen of angels, preached unto the Gentiles, believed on in the world, received up into glory."
Luke 15:10 "Likewise, I say unto you, there is joy in the presence of the angels of God over one sinner that repenteth."
Angels are said to be spirits and are referred to as sons of God because they are direct creation of God.
Psalms 104:4 "Who maketh his angels spirits; his ministers a flaming fire:"
Hebrews 1:7 "And of the angels he saith, Who maketh his angels spirits, and his ministers a flame of fire. 14 Are they not all ministering spirits, sent forth to minister for them who shall be heirs of salvation?"
Job 38:7 "When the morning stars sang together, and all the sons of God shouted for joy?"
Sometimes in scripture, angels are referred to as stars. The star in Matthew 2:9 is an angel because it stops over one house in a small village.
Matthew 2:9 "When they had heard the king, they departed; and, lo, the star, which they saw in the east, went before them, till it came and stood over where the young child was."
Revelation 1:20 "The mystery of the seven stars which thou sawest in my right hand, and the seven golden candlesticks. The seven stars are the angels of the seven churches: and the seven candlesticks which thou sawest are the seven churches."
Revelation 9:1 "And the fifth angel sounded, and I saw a star fall from heaven unto the earth: and to him was given the key of the bottomless pit."
Angels have spirit bodies and are sometimes invisible to physical sight.
2 Kings 6:15 "And when the servant of the man of God was risen early, and gone forth, behold, an host compassed the city both with horses and chariots. And his servant said unto him, Alas, my master! how shall we do? 16 And he answered, Fear not: for they that be with us are more than they that be with them. 17 And Elisha prayed, and said, LORD, I pray thee, open his eyes, that he may see. And the LORD opened the eyes of the young man; and he saw: and, behold, the mountain was full of horses and chariots of fire round about Elisha."
The Angel of the Lord is an appearance of God(Acts 7:33-35, Exodus 3:1-6, Judges 6:12-16, Acts 27:23). Michael the archangel shows up when there is a fight(Jude 1:9, Revelation 12:7), while the angel Gabriel shows up to tell people messages from God(Luke 1:19, 26).
Angels have supernatural strength, invisibility, healing, wingless-flight, ability to control animals (Dan. 6:22), telekinesis (Acts 12:7-10) and ability to control elements (fire, water, air).
Finally, Angels have self-awareness(Luke 1:19), moral awareness(Matthew 13:41), desire(1 Peter 1:12), emotion(Job 38:7) and accountability because they have free will(1 Cor. 6:3, 2 Peter 2:4). They are also innumerable(Psalms 68:17, Daniel 7:9-10). Angels are able to eat, but do not have to eat in order to survive (Gen. 18:8, Ps. 78:23-25).