There are some better pictures out there, but I'm just going to post some of my past tarantulas.

Mating hook of a mature male



spermathecae of a male



spermathecae of a female



Looks like thats all I have, let me know if you have any questions or want links to know how to sex from either of the 2 ways. If you only have one tarantula it might not be that important for you to learn how to sex those ways, and just looking out for mating hooks may be the easiest thing for you to do.