Vim editing cheatsheet
Vim editing can be a pain in the arse, but you pretty much need to know it to do anything on the server properly. (I know, there are alternatives like nano, but pretty much all the examples use vim)
Go for a cheatsheet. Old, tried, and true.
By the way, nano is much easier though, and it lists the commands right in front of you. Awesome. To use it type nano and then the name of the file in you server terminal.
For example,
nano /etc/ssh/sshd_config