I'm not sure if this post goes here and also I won't be talking about ROMS.

I want to create a Pokemon fan-game on Rpgmaker XP but I'm a noob at it.

Any advice on where to start or what I should learn?

You sure are all over the place, aren't you?
Well, If you want to make a fangame, I say ask Randoguy101. He's used to that kind of stuff.

If you're trying to make a Pokemon fangame using RMXP, first download Poccil's Pokemon Essentials. Warning, it's fairly difficult to use, so try to get a handle on RMXP first.