its not as easy as you think. if you're a guy at least.
you need to look up adult talent agencies. or be lucky and be "discovered."
if you really want in, start in gay porn. its easier to get into and you'll have a cock, er i mean foot in the door. (*cough*back door) ok ok im done.
seriously though, you need to know someone. or just be hot or gay or have a nice cock or cum a lot. look up agencies and email them. though im sure they get tons of email from guys looking to get in.
unless you're a girl, then take nakie pics, and send them in.