Mac – How to get rid of black stripes in the bottom and top of screen in full screen mode

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.

MacVim forks (spawns a new process) to launch external processes, but it waits for the external process to return before resuming execution. Thus, killing MacVim simply detaches the child process (your program) from MacVim and attaches it to the main process running, in essence, OS X on the whole.

You have to quit, or Force Quit, your program explicitly in order to kill it.

It's also very likely that if you kill your program, and NOT MacVim, you can continue using MacVim without issue.