Hello, 
 
I want to trade pokemon cards with other people, but I don't know how to do that!
If you know please reply!

Trading cards you can click on someones profile.  Next click on their offers, requests, or contact.  Then you can send a proposal by clicking on the cards you want and have (do this by clicking on the little box to the right on the card).
 
-KingBob

how do you mail it to them?