For acting, you don't really need a portfolio. You need a headshot with your resume on the back. You need to put your name and contact info, any union affiliations (SAG, etc). Then by category (Film, TV, Theatre, Commercials, Various) list your work - name of production, role, studio/theatre/TV channel/client. Below that you list acting courses you have taken and any special skills (stunts, foreign language, juggling, martial arts or anything else that might make you stand out)
For modeling you don't need a full portfolio if you haven't done any professional modeling before. If you get an agent, they will help you put together a portfolio. You will need a good headshot, profile shot, and full body shot that shows off your body - you could do 2, one clothed and one in a swimsuit or underwear.
