This isn't a course on Neovim (we'd need at least 420 more lessons for that), but let's at least figure out how to edit a file and exit the program.
Don't be fooled, exiting Vim (or Neovim) is one of the greatest hurdles you must overcome as a developer. It's a rite of passage. It's a badge of honor.

There's a public file containing a company password!
It's a text file that's using markdown syntax. You can open a file with Neovim by passing in the file path as an argument:
nvim FILEPATH_HERE
Once it's open, you might notice that you can't type anything. That's because you're in "normal" mode, the mode for navigating and manipulating text.
You've successfully edited a file (and escaped from) Neovim!