Hi Mandy,
The Epcot Passport is a fun, rather inexpensive souvenir that makes traveling around the World Showcase a lot of fun. You can purchase a passport at just about any shop in Epcot. They're usually located near the cash register, but ask a cast member if you don't see them. As you travel to the different countries in World Showcase, you can have a cast member write a message in their native language. In the shops they will also stamp your passport. It makes a great keepsake!
There is a lot to do in Epcot. While spending 2 days in this park would allow you to more fully enjoy Epcot, you can certainly see the highlights in one day.
Some of my favorite attractions include: Spaceship Earth, Soarin', The Seas with Nemo and Friends, Ellen's Energy Adventure, The American Adventure. You'll also have fun touring World Showcase with Kim Possible World Showcase Adventure (although, this will soon be changing to a
Phineas and Ferb themed attraction - either way, it's a lot of fun).
Be sure to see Reflections at the end of the day. It's a beautiful show that will cap of a fun-filled day in Epcot.
Hope this helps. Have a magical vacation!