Editing happens in your browser. Auto-save to cloud (in Settings, under Character & saving) writes your build online about a minute after you edit, once a valid IGN is set; with it off, saving is manual. A character that shows Not synced exists only in this browser; after a save the status reads Synced just now or Synced Nm ago.
The top bar holds the manual actions: Save (or Load character when no character is open), Sign in, and the character menu — the character's name with a ▾ — with Restore from cloud, Add character…, Switch character, and Claim this character.
Moving to another device or browser? Load the character or restore from cloud before you start editing there. If the cloud copy is newer than the one on this device, the background auto-save pauses instead of overwriting it — restore or load first, then continue on the up-to-date copy.