"My teacher teaches piano and guitar."
I was replying to this statement: << 'Mo' is more like "my teacher also teaches piano and guitar' along with what ever else she's teaching me. >> I don't fully understand yet what the sentence is supposed to say, but if that statement is correct it is similar to the usage of や. If it's not correct, I don't understand the nuance of も and how it is different from や or と
1) Yes, that's right.
2) You're correct. It's [(apple)も][(orange)も].
In my example, も is just listing what were eaten aside from what was probably mentioned before.
A: I ate only the bananas.
B: You ate the apples and oranges too.
The "appleも" and "orangeも" have no effect on each other.
The "mo + mo" structure is kind of like the English "both + and" structure.
"....piano MO gitaa MO oshie masu." --->
"(My teacher) teaches BOTH piano AND guitar."
But it also leaves it open to include other things. So instead of saying, "She ONLY teaches piano and guitar", it is kind of like, "She teaches both piano and guitar (and maybe a few other things that may or may not have already been mentioned earlier in the conversation)."
There are similar structures in the Romance languages too!