If it’s a fandom it will kind of follow what you or your partner/s kind of want. Like you could do a fandom of Avatar the last air-bender but instead of making an OC/Original Character you can make your own. Other stories are custom made usually to fit a Character sheet that is usually basic.

So you have first or third person pov’s. I haven’t really seen many others other than the one where you act as a narrator. First person is “I grab your hand,” while third person is “he/she/etc grabs your hand.” Second person would usually be talking to someone else or if you are trying to guide them maybe.

Telling the story is the fun part. If it’s a fandom, having knowledge of what it is is kind of important. If you’ve never watched or done anything dragon ball z related, you wouldn’t really know what is going on with the dragon balls or power levels or anything. (I tried that once with limited knowledge and it didn’t end well).
Fiction RP’s are your own or somebody elses ideas that you make custom characters on. The world is generally made up off the top of your head or inspired from something and your story follows soon after.

Now telling the story is like writing a story. If I’m making a post, I write it out first person then I change all the I’s and Me’s to him or his and switch out I say to Crandall says or whatever name. First person stories don’t have “he watched her through her window.” Unless it’s kind of being narrated or moved to another segment or something. First person Rp’s are usually only “I watched her or you through the window. Following your movements anticipating my strike.”