I have tried to follow the following:
How to delete selected text in VI editor
but
5dd
gives
E492: Not an editor command: 5dd
I then tried:
5d
Which only deletes a single line. How can I delete multiple lines?
Sounds like you're entering the commands in command mode (aka. "Ex mode"). In that context :5d
would remove line number 5, nothing else. For 5dd
to work as intended -- that is, remove five consequent lines starting at the cursor -- enter it in normal mode and don't prefix the commands with :
.