Your own address
Your game's site can live at your own domain, like www.yourgame.com. Add the address on Launch › Website, put two records at your registrar, and Tinderbox Works checks them, serves the site there and gets its certificate. If a record goes missing later, you hear about it, and the site stays up at its own name meanwhile.
New
Two records, copied.
Add www.yourgame.com and copy two records into your registrar's DNS: a TXT record that proves the domain is yours and a CNAME that points it at your game's site. A guide per registrar covers TransIP, Namecheap, Porkbun, Cloudflare and the rest, and how to forward the bare domain to www.
Checked, then served.
Tinderbox Works checks the records every 5 minutes while you set it up (or now, with Check now) and says what's wrong in words: a CNAME that points elsewhere, an IPv6 record that's in the way, a CAA record that doesn't allow Let's Encrypt. Only when everything is right does the address go live, with its certificate.
Kept an eye on.
Once live, the records and the certificate are checked every day. If the domain stops pointing at your site, you get a mail and have 7 days to fix it before the address stops being served; fix it later and it comes back with Check now.