Terminal ends with [process completed] and wont let me do anything.

This can happen if a GUI app launched a Terminal session to run a script, or if you double-clicked a command line utility in the Finder. Once the command line utility has terminated, you will get this screen under these circumstances. Just close the Terminal app or just this Terminal window.

Typing exit (or control+d) in the Terminal, or having it in your SHELL dot file — ends that Terminal session and depending how your Terminal settings are configured, you will see [ Process completed ], or the Window itself will vanish — though the Terminal application will continue to run in the background.

You do not want the command exit in any dot file.

Open Terminal settings and make sure there isn’t a command set to run on startup and also check the default profile for the same thing in the shell tab.

If nothing is set in both locations, then it could be in one of the config files.