I'm new here
Hey there! Welcome to RPOL.
First - again - welcome! Seriously. Happy and fun community here.
Second - this site operates quite a bit differently than a lot of other PbP sites. And, it's for the better (it's very logical here.)
PLEASE PLEASE read the "FAQs" in the top-right, it will guide you through almost every question.
After that - peruse the "Wanted - GMs" and "Wanted - Players" areas. You will see people advertising tons of games of all different stripes (with a convenient filtering system). Thousands of systems are represented, though you will see a huge number of DnD/Pathinder games - so no worries about finding something you like.
Not everyone uses a concrete system, and not every GM even uses the same system for deciding with whom to play.
First term to learn: "RtJ" or RTJ - "Request to Join". You will see different games looking for different things - some want to know if you have a character in mind, some just want to see if you can write in the language in question.
Have fun out there and ask questions!