How do I point my own domain at my server?

Open your server and click Domain in the sidebar - it's its own page, not part of Settings. The panel shows you exactly which DNS records to add, with copy buttons for each value.

For a subdomain (e.g. play.yourcommunity.com), add a CNAME record pointing at your free server address. For an apex/root domain (e.g. yourcommunity.com), use an A record instead, since CNAME records are not valid at the root of a domain.

For Minecraft, also add the SRV record the panel shows you, so players can connect without specifying a port.

After adding the records, click "Verify DNS" in the panel. Propagation can take anywhere from a few minutes to a few hours depending on your DNS provider; a shorter TTL (300 seconds) while you are setting things up means quicker verification, and you can raise it back to something like 3600 seconds once everything works.

Do not remove your free subdomain until the custom domain has verified successfully, in case you need to fall back to it.