What are guys thinking half the time?

Question for all you mothers out there:
What is the difference between guys and girls?
Very broad question, I know, but I really want to hear what your opinions are on this subject. See, today, I hung out with a guy (which I don't normally do, like ever), and he asked me to the school dance as friends. We talked a lot about guys vs. girls. 
Who's simpler? Who is more analytical? What will make a girl cry? Why do guys do outside of school and what drives them to do it? What will make a girl forgive you? What are the rules that guys have for each other concerning girls? And vice versa. 
 It was really interesting to hear the guy's perspective on all these things. I mean, what are guys thinking about all the time? Seriously. They may seem very non-complex, but at the same time, us girls never seem to understand them. They flirt with us, then go out with someone else. They tell us to go away, then ask us out. I don't get it. It's a lot like the movie "He's just not that into you." 
 But really, this time I need some advice and some answers from you! Help me out here. And if you have a teenage son, tell him to communicate not just over text, but also in person and to give girls chocolate! That's what gets us!! And for the mothers with daughters, tell them not to overanalyze every word that a guy says and every little thing that he does. If he brushes back his hair with his hands or just shakes his head to get it to move out of his eyes, it probably doesn't mean anything different. I learned that much today at least.