Cannot join any servers besides suggested ones

When I got to servers and press add server and put in the server ip (yes it was correct-I tried it with many different ones multiple times) and it will say locating server forever. It won't ever connect and I do not know how. The featured/suggested servers still work, so I don't know what the problem is. I don't know if it has to do with the "port" thing at the bottom.. I don't know what that is... Yea I might just be really dumb but please help I want to join other servers!