NOTE: Specific examples given for options, flags, commands variations, etc., are not comprehensive.
Vim has 2 main "modes", that chance the behavior of all your keys. The default mode of Vim is Normal Mode and is mostly used for moving the cursor and navigating the current file.
Some important (or longer) commands begin with ":" and you will see the text you enter next at the bottom left of the screen.
:q[uit] - quit (the current window of) Vim. ("Window" here is internal to Vim, not if you have multiple OS-level windows of Vim open at once.)
:q! - force quit (if the current buffer has been changed since the last save)
:e[dit] {filename} - read file {filename} into a new buffer.