The kinds of things you'll need to include in your portfolio depends on the course you're applying for. You can review specific requirements on the college's website.
In an art portfolio, you'll need to include things like: preliminary sketches, observational drawings, finished pieces and final outcomes. Illustrations can be digital or hand drawn. We also welcome paintings or colour work, to show how you can use, mix, control and communicate with colour. You want to show a range of techniques and processes. If you do 3D work, then adding photographs of your work is a good way to showcase it.
Remember, it's about quality not quantity.
Be prepared for a live interview to talk about your art, inspirations, and processes.