My knowledge of command line Linux was pretty limited to changing ownership of files, using wget and configuring Apache but like yourself my knowledge of setting up email and whatnot was flaky.

Fortunately, you're in luck. I learned everything about managing a VPS from Linode's own excellent documentation. This is the guide I used for setting up mail: http://library.linode.com/email/postfix/gateway-ubuntu-10.10... — bit out of date, but still relevant I am pretty sure and worked for me when I needed it.