The canvas is in limited beta — not yet open to everyone. If it isn't available on your account, the regular create forms do everything the canvas does, just by hand. (When it opens up, this guide gets updated — that's a promise the docs keep.)
The create canvas is for the moment when something happened and you have material — notes on your phone, photos, a voice memo, a flyer, a link — but not a finished piece.
Drop everything into the canvas. It reads what you gave it, figures out what you're probably making (a story? an event? a classified?), and fills in the form for you. You confirm the type, edit anything directly, and publish through the same flow as any other content. Audio gets transcribed; what you drop stays yours to show or keep as background research.