Help me petah, my grandma sent me this and I might be stupid

Peter, I’m lost

Peter why do the mountains have lines drawn on them?

Petah why are Grimace shakes bad?

Petah, i don't get it

Ohhh petaaa

petah what does this joke mean?

I don't get it. Peter, could you help me?

Petah help, Is the joke just that OP thinks its bad?

Peter please explain whats going on here.

Petah