It does indeed sound like a permissions issue.
You'll need to get into root user either directly
and give root passwd, or use sudo
and give your own passwd.
Always backup a file before editing.
As above, editors are a matter of personal choice, although I will point out that vi has been the default guaranteed-to-be-installed editor on just about all forms of *nix for years if not decades now (inc rescue situations).
Well worth learning the basics just in case your favourite other editor is not available.
Personally I'm happy to stick with vi/vim ..