The word "angels" literally means messenger. Angels are a race of created beings much more powerful than man, although they are infinitely less powerful than God.
Let's begin with a clarification from Exodus:-
"For [in] six days the LORD made heaven and earth, the sea, and all that in them [is], and rested the seventh day: wherefore the LORD blessed the sabbath day, and hallowed it." - Exodus 20:11
God created -everything- in that same week - this has to include all the angels. Thus, the angels were also made on one of the six days of Genesis 1. On which day were they made?
In Job 38, God demands Job:-
"Where wast thou when I laid the foundations of the earth? declare, if thou hast understanding. Who hath laid the measures thereof, if thou knowest? or who hath stretched the line upon it? Whereupon are the foundations thereof fastened? or who laid the corner stone thereof; When the morning stars sang together, and all the sons of God shouted for joy?" - Job 38: 4-7
God is using figurative language here. The morning stars are a figurative way of referring to the sons of God, which refer to Satan and other angels (Job 1:6) What exactly are the foundations of the earth? I honestly do not know. I see two ways to interpret this verse:
So much for the creation of the angels. The next thing to learn is that God will not make evil entities:
"And God saw every thing that he had made, and, behold, [it was] very good. And the evening and the morning were the sixth day." - Ge 1:31
Thus, even the angels were "very good". The chief angel is Satan, also called Lucifer (the Shining One). In particular, Satan was a really special character:-
"Thou hast been in Eden the garden of God; every precious stone was thy covering, the sardius, topaz, and the diamond, the beryl, the onyx, and the jasper, the sapphire, the emerald, and the carbuncle, and gold: the workmanship of thy tabrets and of thy pipes was prepared in thee in the day that thou wast created. Thou art the anointed cherub that covereth; and I have set thee so: thou wast upon the holy mountain of God; thou hast walked up and down in the midst of the stones of fire. Thou wast perfect in thy ways from the day that thou wast created, till iniquity was found in thee." - Ezekiel 28: 13-15
Thus, Satan was created good, but later became evil. How did it happen?
"For thou [Satan] hast said in thine heart, I will ascend into heaven, I will exalt my throne above the stars of God: I will sit also upon the mount of the congregation, in the sides of the north: I will ascend above the heights of the clouds; I will be like the most High." - Isaiah 14: 13, 14
Satan, the crown of God's creation wanted to usurp His position! Satan's fall disproves the theory of the humanists that all bad behavior is due to negative circumstances. Satan had everything going for him, yet he did what was wrong. Satan was obviously motivated by arrogance and pride, but his rationale is something of a mystery. Did he really think that he would be able to dethrone his Creator? But how did Satan know that he was created? God must have told him. Here's an interesting possibility. Satan may have doubted God's word to him. If (so Satan must have thought), God did not really create me, but both of us have sprung out of nothing, or of some primeval matter that has been existing for eternity - it's just that He sprung into existence before me. If this is the case, I can probably fight God for supremacy and win! May be we can ask God when we meet Him, whether Satan actually thought on these lines, but in the meanwhile, it's interesting to note how the creation myths of some cultures describe gods arising out of primeval matter.
Satan was probably joined in his rebellion by one third of the angels (see Jude 1:6, Revelation 12:4).
God cast away Satan:
"And Jesus said unto them, I beheld Satan as lightning fall from heaven...How art thou fallen from heaven, O Lucifer [literally: Shining One], son of the morning!" - Luke 10:18, Isaiah 14:12
When did Satan become sinful? The Bible does not give us the exact time. But we know that Satan tempted Adam and Eve, and they fell into sin, and then their son Cain was born. Seth was another son younger than Cain (Genesis 4:25), and Seth was born when Adam was 130. Thus, Satan surely became evil less than 130 years after he was created.
What do Satan and other angels do today? The answers are evidently different for the good angels and the bad angels. The Bible does not have much to say, but gives us some hints.
Good angels will be part of the great company of God for all eternity, along with those of us from mankind who have been redeemed. The bad angels are headed for hell (Matthew 25:41). It's interesting to note that Matthew 25:41 mentions hell as being prepared for the devil and his angels. People are also headed there. God does not want any human to go there, but if a person does not believe in Him, there is no other place fit for him or her.