I need a wiring diagram for a bathroom, including a GFCI receptacle and a double gang box with two switches - one controlling the vanity light and one controlling the exhaust fan.
It sounds like you're not experienced in electrical work. I'm sure you wanted to do this yourself, but I would recommend that you leave the electrical work to a professional.
If you need to ask for the entire wiring diagram for a bathroom, it indicates you're not familiar with the NEC. If you use incorrect wire sizes, circuit breakers, or do one of thousands of things wrong you could burn down your house or kill someone.
Be smart and safe and call a certified electrician.
This is too broad for us to really answer, and suggests a knowledge gap in key places.
It's tough to know "what you don't know", and Google really, really does not help. Search engines answer questions, and they just don't work unless you already know which questions to ask.
I suggest visiting a library, and browsing their how-to books on home electrical. Find one that feels accessible to you, and here's the important part, read it cover to cover. Don't flit around only reading the parts you think are important, because you actually do not know that.
That gives you a well-rounded coverage of the field. You will still have more questions, but this will give you a framework from which to ask them.