Base running can be confusing at some times. If your playing with friends and someone hit a pop fly, you shouldn't run. For instance, if you were on first base and started running before the player catches the ball, they could tag first and you would be out. However, a way to get around is is to tag up. Tagging up is when you let the player catch the ball and once the player catches the ball you can run to second. You can still get out if you don't run to second fast enough they can tag you out.

Stealing rules are different in different leagues. In mine, you can't start stealing until the pitch crosses the plate. The key to stealing is getting a good jump if don't get a good jump you may get out.
The in field fly rule is very confusing. Wikipedia has a good definition.
If you didn't understand my rules to tagging up wikipedia has a good description.