Someone gave me an IP address for their server. How do I join it?

From AAManual

To join a server by IP address, click on Deployment, right click on the server browser and click the 'Open IP' option. You will now see a dialog where you can enter the IP address.

Alternatively, you can open the console (~ or tab keys), and type:

start x.x.x.x (x.x.x.x being the IP address of the server)

If the server has a password use the following procedure to join : open the console (~ or tab keys), and type:

start x.x.x.x?password=PASSWORDHERE

(x.x.x.x being the IP address of the server, PASSWORDHERE being the password).