URP doesn’t have fixed rules, but there are some guidelines to make the RP fun for everybody. Don’t worry too much if you accidentally break some unwritten rules. You are new to RP, that’s completely normal and fine.
Don’t mix up your character and yourself (=the player). The usual beginner mistake here is: You see names hovering over people’s heads, but your character cannot. So let your character ask for them. And, also important, if somebody’s character insults your character, they are not insulting you!
Everyone has the last say about their character. E.g. if somebody wants to steal your purse, they are only attempting it and you write if it works out.
Fun is above everything else. Roleplay is not about winning, but experiencing awesome stories together. Don’t make yourself overpowered and instead let others shine. Not all playstyles are compatible, and it is fine if you don’t want to play with some people. And give others time to type, so they can participate. <3
That’s enough to start, but you can read more about RP etiquette (link) and common beginner mistakes (link).