Job 38
God is talking to Job, and tells him to man up! He says where were you when I made the world, because Job was questioning him. Then God goes on to say how he made the world, and how powerful he is to show Job that he knows what he is doing.
Job 39
God is continuing to tell Job about his knowledge and power and ask him questions to show Job how powerful and intelligent God really is. He wants Job to know that God knows what he is doing, that he will provide and help Job in his time of need.
Job 40
Job then tells God that he is vile and that he is sorry for what he has done. He knows that God is all powerful and all knowing. He knows that he has no right to question God, and he apologizes to God for what he has done.