Go online, find the server you want, such as search up 'the Archon ip' or 'the Archon ip adress', and you should find some websites that will have something like:
Server Name: The Archon
IP: pvp.archonmc.com
Copy the IP, and go to minecraft. Open multiplayer, and press 'Add a Server', then put the IP address in, and the name of the server (don't worry, there is no specific name for the server name section. but most players just put down the server name.) Here's a good website for IPs:
http://minecraftservers.org/
Hope I helped!