How To Open a Port

You can open a port by heading to the Network & Ports page under Advanced. Here you can open a random port for your server by pressing the Open Port button.

Why Random?

In most cases you don't need a set number, as the port number can be changed in the configs. Minecraft plugins for example always have a config you can set the port number in. Random ports are used as unless you have dedicated IP, more than one client will be on the same IP.

If you own a dedicated IP, you can set a number of your choosing by opening a support ticket.