If you like the flavor but not the heat of those chiles used in Mexican food, you can reduce the heat somewhat simply by taking out the seeds and the interior ribs. The majority of the heat is in these portions of the chile. Finally, very carefully remove the inner skin with a knife; that's where most of the rest of the heat is.
If you like hot peppers with your Mexican food, be careful not to get addicted. The pain from the pepper's heat causes your brain to release endorphins, natural pain relievers that are related, chemically, to opiates like morphine. After a while, you might start eating hot peppers just to get that endorphin rush!