Relations, functions and ordered pairs.

Hello all and thanks in advance for all of the help you'll be giving me for the next couple of weeks. I'm just finishing a college algebra class and admittingly I haven't been the best student. The class is mostly online, that coupled with most of the in-class teachings consisting of calculator help (and the teacher stated at the start of the semester that she doesn't know how to use a Ti-89, which I have and I didn't want to buy another calculator after spending 130+ on mine) leaves me basically on my own. She (the professor) was nice enough to give us a review for the final exam (which I'll be asking plenty of questions about in the future) as well as a 3 question take home exam; which is where my first question is coming from. Anyway sorry for the long introduction, my first question from the take home exam:

"1. One way to define a relation is "A set of ordered pairs".

a. Give an example

b. What is the difference between a function and a relation? Is your example in part a) a function? How can you tell?"

I've scored fairly well on most of the assignments/test/quizzes thus far, but for some reason when I look at this take home exam it looks alien to me. Thanks for any replies.