Welcome to the website, RosebeltAngel! Have you written before? That might help you get an idea of what you're comfortable starting with in terms of length and what section to start with. Free roleplays tend to be a few sentences, Casual roleplays tend to be a few paragraphs or more, and Advanced roleplays tend to be very long posts. What I would maybe if you don't know what you're comfortable with is skim a few Free and Casual roleplays if you're not sure what post length you're comfortable with.

I hope that helps you a little and that you enjoy your time here!