Give a user 'sudo' access by adding them to the 'sudoers' file

This is usually done by running the command 'visudo' as root.  That
will bring up an editor, and all you have to do is add a new line
similar to the line already there that reads "root ALL=(ALL) ALL".
The new line will be the same, except instead of "root" it'll say
"jrandom" or whatever the new username is.

The editor invoked by visudo may or may not actually be 'vi'.  If it's
some other editor, there are usually on-screen instructions telling
you how to use it.  Note that the default non-vi editor is sometimes a
Pine-like interface, and when you tell it to save, it will claim it's
saving to "/etc/sudoers.tmp".  That's okay, just accept it -- that
file will get moved to sudoers when you exit visudo.

If it is 'vi', here's what you need to know:

Use arrow keys to navigate to the end of -- i.e., on the last
character of -- the line *above* where you want to insert the new
line.  Hit 'a', which means append-and-insert.  Now you're in
insertion mode.  Type a newline to create the new line, type out
"jrandom ALL=(ALL) ALL", then hit ESC to get out of insertion mode.
Now type "ZZ", that is, Shift-Z Shift-Z, to save and exit.

(Note you can specify the editor by setting the $EDITOR environment
variable.)