A query port is how the game can connect with steam to allow it to show up in the public list.
1 Login to the Kinetic Panel
2 Head to the Network & Ports tab on the left hand side.
3 Click on the "Open Port" button.
4 Now, copy that port you opened & give a note of "Query Port" so you can remember what it is.
5 Head to the settings page & paste that port in the "Query Port" box, then start your server.
6 Now, when adding your server on Steam, put ConnectionAddress:QueryPort. Then, when the server is online, it should show up there.
That is how you set your query port on your rust server.