Well do you have to write about two people you personally know? If so, think of two people in you know, your first paragraph could explain who these two people are and why you chose them.
The second paragraph would be about how there are similar: backgrounds, education, habits, personalities,etc...
Third paragraph on how different they are, in what areas are both complete opposites?
Based on the info you have given, that's what I'm guessing you have to write on. If you have more information on the essay topic you should post it here! Hope this helps and gives you a start!