To start RPing you need to create a character. You do this by opening a topic here in the Character Creation section. Put the character's name and desired village in the title (or missing nin) and wait. If you want to create a ninja profile with age and appearance and hobbies and history and that kind of stuff, that's entirely up to you. A ninja profile is completely OPTIONAL.

First timers are advised to choose a village rather than become missing nin right from the start because the first characters always start with 0 money and 0 ninja level and a missing nin that weak won't last long.

Anyway, if the village you are petitioning accepts you, they will create an account for you in their shinobi shop. Unlike the ninja profile, the account is mandatory and this is where all your jutsus and items other stuff will be listed. This is the default look, but if you don't like how it looks you can sent a village council member the code for how you do want it to look like:

Spoiler:

To obtain a jutsu or weapon, just go to your village's shinobi shop, choose something from the list and post that you want to buy it (but check first to see if you have enough money to buy it). If you want a canon jutsu or weapon that's not on the list then post a link to its description on leafninja.com or naruto.wikia.com so that the staff can adjust it to the system first.

If you want a custom jutsu, item or skill, then open a topic and post them, then await approval. Note that custom stuff are more expensive that the stuff in the shinobi shop, so check how much money you have before asking for custom things.