Use MacVim as standard Terminal?
You're confusing the terminal with the text editor, as other commenters have pointed out. Still, there are a number of ways to make the terminal more vim-like, or vim more terminal-like.

If it's vi-style keybindings in the terminal you're after, add set -o vi to your ~/.bash_profile (assuming you're using bash). This will allow you to use vi-style keybindings at the command line (hjkl movement, modal editing, etc.)

If you just want to be able to execute unix commands from within vim, prepend ! to the beginning of those commands at the (Mac)Vim command line. For example :!pwd will print the working directory.

There are also plugins like Conque which allow you to run a shell from within Vim, which sounds like it may be exactly what you're after.