To find this "server address" box first click “Multiplayer” in the Minecraft game menu and click "Add server". Now you can type the server IP address in the "server address" box. Click “Done” and then click “Join Server”. If you did everything correctly, you should be connected...
You should be in the Minehut lobby. From there you can type /join HellowBR and the server should start for you. Then once you're in the server, you can get more players to join by advertising it in the Minehut lobby by doing /ad!