Your address is shown at the top of the server panel: yourname.arcadeservers.com. Just click the copy button next to it.
Open Minecraft Java Edition → Multiplayer → Add Server → paste the address. No port needed; the default port is used.
Make sure your game version matches the server version. You can see the server's version in the Overview tab; pick the same version in your launcher if needed.
If you can't connect, first check the server shows 'Online'; press Start if it's stopped. If the issue persists, check the last lines in the live console — most connection issues reveal themselves there.