IMAP is POP mail with a twist. It is like POP in that it uses a central mail server that receives and distributes the mail, but it also includes a way for a person's mailbox to following him or her. Your Unity account gives you an Internet address that consists of several parts, each separated by a period. An e-mail address works just like a normal postal address. From left to right, it moves from most specific component to the most general.
Postal addresses do the same listing specific persons, street address, city, state, and country.
NCSU's domain is edu, as are all educational institutions. Unless you're sending messages to another country you'll probably never use or see this. Often there will be more than one part to the site. Fortunately, though, most mail programs automatically attach your e-mail address to your messages, in a way similar to the way phone system's Caller ID works. However, these days with so many new people getting on the net all the time, sooner or later you're going to want to look up an old friend, colleague, or acquaintance, and they aren't going to be around for you to ask.