QA vs q!
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Hit the Esc key to enter "Normal mode". Then you can type : to enter "Command-line mode". A colon (:) will appear at the bottom of the screen and you can type in one of the following commands. To execute a command, press the Enter key.
:q to quit (short for :quit)
:q! to quit without saving (short for :quit!)
:wq to write and quit
:wq! to write and quit even if file has only read permission (if file does not have write permission: force write)
:x to write and quit (similar to :wq, but only write if there are changes)
:exit to write and exit (same as :x)
:qa to quit all (short for :quitall)
:cq to quit without saving and make Vim return non-zero error (i.e. exit with error)
You can also exit Vim directly from "Normal mode" by typing ZZ to save and quit (same as :x) or ZQ to just quit (same as :q!). (Note that case is important here. ZZ and zz do not mean the same thing.)
Vim has extensive help - that you can access with the :help command - where you can find answers to all your questions and a tutorial for beginners.
IK