Welcome
In general, keep track of this thread, where new games are announced and requests for replacement players are announced as well.
See one you like....post your characters profile (make sure it satisfies the DM'S character creation guidelines)... get chosen, have fun....or not, keep trying!!
Play-by-post games are somewhat difficult to get into. I'd recommend checking the recruitment subforum (where this post was made) regularly for a starting campaign that interests you. Once you find one, I heartily recommend creating a new character for it, tailored to the needs of the campaign, instead of trying to force an existing character in. Most of these campaigns are not first-come-first-serve, so you have to establish something that makes your character special that will make the DM select you.
If you have difficulty, I recommend establishing some PBP credibility by creating your own game as a DM/GM.
PBP is a fantastic format for really exploring a character. You'll have a lot of fun. Have fun and good luck!