@Lexie,
Hi Lexie, and welcome.
Oooh, it's been a long time since I was an art major. My first questions are the same as sullyfish's -- do they have guidelines? They must, of some sort.
What I remember is something like this, for 2-D artwork (drawing, painting, etc.):
http://www.dickblick.com/products/pina-zangaro-vista-packaged-screwpost-portfolio-books/
If you have 3-D artwork (or really big 2-D artwork) you'd need to have good photos of it, probably from a few angles.
Aside from those basics, I remember being advised to tell a story of some kind, whether of your personal development as an artist, or as you explored a theme, or even by color/ subject matter.