To enforce means to make sure the laws and rules are being followed. So those guys wearing striped outfits and whistles? They're in charge of enforcing the rules of the game.
See the word force inside of enforce? It can help you remember that enforce is all about forcing others to follow the rules. The traffic police enforce the driving laws by handing out speeding tickets. Your parents hopefully enforce good behavior by grounding you when you stay out too late. It would be wonderful if everyone just followed the rules on their own, but it seems the temptation to be bad is just too strong. So thank goodness for all the enforcers that keep us in line.