Pair your TV
The Qelvue app on your TV shows an 8-character code. Type it here with the address of your MediaHub, and you approve it on your own server.
Why you approve it on the server
Qelvue's website has no account of its own, so it cannot sign a TV in. Your MediaHub holds the accounts and profiles, and its approval page is the only place the code is checked. Nothing is linked until that page says so, and the code stops working after 15 minutes or one use.
Self-hosting? The setup steps are in the MediaHub docs.