How to hang a 42 inch plasma TV on my wall?

Can anyone who is a wall expert explain me the specifics in doing that cause i am trying to do it myself.Basicly i have a 42 inch plasma television.And i’ve not bought the wall mount brackets yet.Once i get the right one, what do i have to do?I know i can’t just nail/or screw it to my dry wall.How do i safely mount it so that it stays on some beam or something in my wall.Hope you understand what i mean.Calling the proffesionals is gonna cost about 0 to 0.