I know this seems like it might be a wierd topic - when would you ever need to relate a table to itself?
Well, I can think of two real good examples. The first was actually sent in to me from a customer... you have a table of PEOPLE, and you want to indicate which one of those people is the head-of-household of a family. The family members are also PEOPLE.
Now you can relate the table to itself by specifying a head-of-household for EACH family member.
Also, what about genealogy databases where you have PEOPLE, and each person needs a father and mother... who are also PEOPLE records?
There are lots of uses for this, and I really haven't covered this in any of my tutorials, so here's a free video for the Tips & Tricks section that covers this:
/tips/access/relating-a-table-to-itself
Enjoy! Let me know if you like it.
UPDATE (6/22/2012): I've now covered this topic EXTENSIVELY in my Access Relationships Seminar.