Your faces live with your watch, so this page has to be opened from it. Typing the address on its own cannot tell which watch you are.
That is not a watch link. Copy the whole line from the watch app's settings.
The identifier alone works too. Either way it stays in this browser until you log out.
Your watch is connected, and has no face on it yet.
Forge your first faceFaces you buy stay here for good. Put a different one on whenever you like — the watch picks it up by itself in about a quarter of an hour.
Forge another faceOpen this on the other device, or copy it across. It connects that browser to this watch.