Adding onto this as I'm running a roleplay at the moment.
It all really depends on the group/roleplay you plan to join. From mapped, non mapped, literate or semi. sited, non-sited, to realistic to semi or non realistic.
Literate roleplays tend to have you post two paragraphs, to be accepted as well as have decent grammar. You may be confused by how to type in two paragraphs when roleplaying I suggest using ">>" at the end of the first one to let them/others know you are posting more, and end it off with "<<" and or -d-.
Mapped roleplays tend to have a map to download when being accepted into the group, from either a public made map or private one the roleplay owner/map maker made for the roleplay specifically. [ most mapped rps are sited but they can also not be sited. ]
Non-Mapped roleplays are normally roleplaying in maps such as flourite plains or ficho tunnel, bonfire island, etc.
Sited roleplays normally have a website from proboards, or weebly, whatever they may use. The sites are useful as you can read information on the roleplay, post biographies, download the map, and read rules of the roleplay you have joins. As well as information on ranks, etc!
Although everyone has said a lot to help ye, I hope this helps some as well?