[SIZE=4]This is accurate as of version 1.4. The way to connect to a server should now be extremely clear and self-evident, so this is no longer going to be updated.[/SIZE]
Start by going to the main menu.
Tap "JOIN GAME".
Tap "ONLINE SERVER".
To connect to a server, you'll need to know two things: the server's IP address or URL and the server's port.
By default, the IP is already entered. The default IP will not work. Any IP beginning with 192 will also not work. You need to find an IP of a server, such as in this forum.
Once you've entered the server's IP or URL, the port (use 15151 unless the owner states otherwise), your nickname, and an image for your avatar, tap "JOIN SERVER".
If the server is whitelisted, you may need to submit a request to join. Some server owners may be contacted by private messaging on the forums. On Blockserver-hosted servers, the world page (the "Info" option on the server list) may allow you to contact the owner.
All Blockheads are linked to your nickname. If you enter another nickname, it is like another profile for that server. Each nickname is linked to your device, but they can be shared between devices if they share an iCloud account, a Game Center account, a Google Play account, or a Amazon Game Circle account.
If you have problems connecting to a server, see Common server connection problems.