how do credit cards work?

[BP-Revo]

I don't know too much about CC cards (I want to get myself one soon) but I do know that you should pay it off every month, cause doing that is what keeps you out of debt and looks good...

I have a card on my parent's CC which they put nearly every charge on. Its been payed off every month without fail for the last 15 years. Apparently, this helps build my credit score as its a CC that has my name on it. My brother has a card too (but my parents just leave it in a drawer at home). He never uses it, yet it apparently benefits his credit score too.

I'm already getting tons of mail offering me credit cards...