"One day the angels came to present themselves before the Lord, and Satan also came with them." NIV translation
Now, the scene shifts from the earth to heaven and we see that all of God's creation must answer to Him. The word translated as "angels", here, is actually "ben" in the Hebrew which means "sons" and speaks of the fact that these creatures were created by God. We are introduced to Satan and, in Hebrew, his name means "opponent" which reminds us of the fact that he organized an uprising in heaven and tried to ascend to God's position but was defeated. As odd as it might seem, this verse should give us all comfort. There are many times when we may feel that things are spinning out of control and often we feel like evil is winning. This verse reminds us that God is in control of all things and even Satan must answer to Him.
"The Lord said to Satan, 'Where have you come from?' Satan answered the Lord, 'From roaming throughout the earth, going back and forth in it.'" NIV translation
God knew what Satan had been up to but asks the question for our benefit as well as for the benefit of the rest of the creatures in heaven.
So, why is Satan our opponent and why does he want to destroy us? He wanted to take God's place but was defeated and cast out of heaven where he had led the worship of God. He hates all men because we have the capacity to worship our Creator instead of him.
"Then the Lord said to Satan, 'Have you considered my servant Job? There is no one on earth like him; he is blameless and upright, a man who fears God and shuns evil.'" NIV translation
Once again, God asks Satan a question that He already knows the answer to and that answer is yes. God holds up Job as an example of the fact that even a man (which was created to be a little lower than the angels) sees that He is the only One that should be worshiped.