This help article assumes that you or another person have already set up a server correctly. If the server in question is not set up correctly, you may not be able to access it. For help on setting up a server, please see the article on help on setting up servers.
Public Servers:
Public servers are ones that are visible to any prospective players on the internet. They are usually accessed via the in-game server browser's "All Servers" tab. They can, however, be joined through IP.
Private Servers:
Private servers usually only show up on your local area network. Whether you have multiple computers connected to the same router, or you are using a virtual LAN like Hamachi or Tungle, these servers are generally not visible to the public, though they are visible to other computers on your local area network. One can usually find a LAN server in the in-game server browser's LAN tab. However, if the server is connected to the internet, players outside your local area network can still join via in-game IP connection.
Direct IP Connection:
If you know the IP of the computer hosting the server you wish to join, you may use direct IP connection to join. This is useful for LAN parties, or when the server list may not be functioning properly due to master server maintenance. To connect via IP, start by opening a console. You can open the console by pressing the tilde key (~) by default. Alternatively, you can open a text chat but delete the "say" command. Once you have a console ready for your command, type in the command like the following example:
(the IP here is just an example, replace it with the unique IP of your server)
open 123.45.67.89
Press enter, and the game will attempt to connect to the server at the given IP. If this does not work, make sure you typed the IP correctly, and that you have the public IP of the server, not the internal IP used by the router (unless you are on the same network, internal IP's are not usable for IP joining). If you are using LAN software like Hamachi, make sure you are using the IP given by the software.