How can I play on a Minecraft server?
Find a server you want to join and copy the IP address. Once you've copied the IP, launch
your Minecraft client, click "Multiplayer", then "Add Server". Then, paste the IP address in and click save. You can also use Direct Connect with the same IP.
Here's a YouTube tutorial for joining a Minecraft Server.
If you have any trouble connecting to the server try these troubleshooting tips.