Sirius Studio publishes with your wallet's key. Sign in on the dashboard, then come back to this name.
Pick a starting point. Everything is editable — drag blocks in from the right, click any text to change it. Nothing leaves your browser until you press Publish; then the page is stored on Sia and the name points at it.
The page and its assets are uploaded to the name's folder on Sia, signed with your key. If the name does not point at that folder yet, one on-chain update sets it (a few cents of chain dust).