Simple: Install Vim on your system, then run the vimtutor program. It will present you with a series of lessons (extremely well-written IMHO) about how to use Vim.
P.S. There is also a gvimtutor but I don't know whether it can be used with macvim. (I think ir does, but I cannot check it because I'm not on a Mac.) If it can't, it shouls work with gvim for X11 but on a Mac this is much less practical.
Best regards,
Tony.