Instructions
Find the address of the "Minecraft" server on which you would like to play. If you are joining friends on their server, ask them for the server address. Otherwise, consult a list of servers, such as the one found on the "Planet Minecraft" website (see Resources) to find one you like.
Download and install "Minecraft" if you haven't already. To do this, download the version of the "Minecraft" launcher that corresponds to your operating system from the game's official website (see Resources) and run it. The launcher automatically downloads all other necessary game files when it is first run and also takes care of keeping the game updated.
Run the "Minecraft" launcher, if it isn't already open, sign in to your game account if you are prompted to do so and then click "Play."
Click "Multiplayer" and then click "Add Server." Type a descriptive name for the server in the "Server Name" field, type the address for the server in the "Server Address" field and then click "Done." This adds the server to the list on the main "Multiplayer" game screen.
Click the server's entry in the list to select it and then click "Join Server" to connect to it.