Hi, Nani! Welcome to RPF! I know there's a lot to take in at first, so I'll give you the basic site overview, and if you've got any specific questions I'm happy to help out with anything. I'm sure you'll get it figured out in no time.
To start off, I'll give you the link to our rules
Check them out when you can and feel free to ask for clarification if you need it. The community here is super helpful and always great about pitching in to help new people.
If you're looking to join an RP, try looking in one of the "Requests" sections - there's one for casual (basic, easygoing RP), one for intermediate (a bit more effort required) and one for advanced (for when you really want to put effort in, but much slower). Any of the recent "REQ" threads in those sections are good places to get started - just take a look and see if you can find something that appeals to you. There's a huge variety of RPs on this site, and you're more than welcome to create one of your own as well.
There are also two other areas - Superhero Sandbox, which is a multi-tier comic-style universe, and a post-apocalyptic area which is just starting up. For each of those sections, you'll create a character (or characters) and weave them in and out through several different storylines. It's up to you which style of RPing is more appealing to you, and of course you're welcome to try both - plenty of us hang out in multiple areas.
I mod over at the Superhero Sandbox, and I promise we're not scary people in there even if we may appear that way. I also hang out all over the place, so I'm happy to answer any questions I can. Feel free to hit me with any inquiries and I'll do my best to answer them for you.
Let me know if there's anything else I can help with, and enjoy your stay!