Hi! Welcome to the site. I can give you some help. First you'll need to get a character in mind, and then head over to the Character Creation area
HERE to fill in the template. If you need help feel free to ask a moderator or admin or anyone that seems to know what they're talking about.
You can play any character that you've made up, so long as they are approved, but if you want to play a character who's canon to the show, you have to make sure they aren't taken first. Ask one of the admin about that, they should have a list somewhere.
In case you have trouble finding it, this is the Character
Template that you should use. Be thorough and fill it out to the best of your ability. It has instructions on how long certain things should be, so don't neglect that or it may get denied. We mostly want to know that you have put plenty of thought into your character and that you know them well enough to play them well, and then the RP sample is so we know how well you roleplay and such