Ensure you are running version 1.21.5 of Minecraft Java Edition. If you are playing vanilla, this will be the default.
Start the game from the launcher
Click "Multiplayer"
Click "Add Server"
In the "Server Address" box, type the server address as shown above.
Click the "Resource Pack:" box until it says "Enabled"
Done! If you have not already been whitelisted, submit your username using the form below.