in steam, click "view" at the top of the window. click "servers". in this window, click ADD A SERVER. add the server IP and PORT. the port # should be 1 number higher than it actually is. for example

if the server you are trying to reach is 123.456.7.89 : 12345

you would add: 123.456.7.89 : 12346

add the server to your "favorites", and now u can join via this window.