What is the proper setup for hooking up mics and instruments to a camera?

I'm new to music tech, so pardon my excessive lack of terminology and "theory". But I believe I have a basic idea of how it may work. What I'm trying to do is plug audio recording devices to my camera(Nikon d5100) for helping a friend record her covers, for she is an aspiring musician. Now the jack on my camera is a standard 3.5mm female. So I need a microphone with a 3.5mm male.
Also, could I hook up a mic and an instrument into a double 3.5mm female hub with a single male(does that make sense?). Would that record correctly?
Mic into Hub
Hub into Camera
Instrument into Hub

Now my friend says her mic can plug into her guitar(an acoustic/electric). She doesn't know if it'll channel her mic to the amplifier. Is that how that works?
Mic into Guitar into 3.5mm jack converter into Camera?
Again I'll remind you I don't know all the correct terms. Please correct any theory. Any assistance you could give me would be most helpful.

That's not going to work. What you should do is record on digital recorder and sync the sound later. You need inputs for each device you are recording and you need to control their levels. It's not hard to do but you need the right equipment.

The big problem with looping audio (trying to sync with video) is the performance is never the same twice.

My suggestion would be, depending on the number of players you have say 4 or 5, perhaps 5
Shure microphones with stands set at their amplifiers. Run those into a Shure mixer and feed that mike level to your camera.

Understand a setup like this won't be cheap but it's about the best. Also you'll need a quiet place like a recording studio so there's no echo or outside noise. A typical building won't work it'll have to be insulated for sound.

This business is complicated but if you want it done right this is the kind of thing you have to do.