You can access portfolios from three places:
Self tab → Portfolios section (your own portfolios)
Group tab → Portfolios section (portfolios shared with that group)
Create tab → Create a Portfolio (work on an existing portfolio)
Teachers also have an additional view: portfolios that are responses to a template they created will appear on the Responses page within that template. (see Where to Find Responses to Your Portfolio Templates).
From the Self tab or Create tab, you can continue editing an existing portfolio or start a brand-new one.
From within a Group, you’ll only see the portfolios that have been shared with that group (via the Sharing settings). Here, you can continue editing existing portfolios, but you can’t create new ones from scratch.