To join a multiplayer server in Minecraft, you'll need to follow these steps:

Open Minecraft APK and click on the "Multiplayer" button in the main menu.

Click on "Add Server" to add a new server to your server list.

In the "Server Name" field, enter a name for the server you want to join.

In the "Server Address" field, enter the IP address or domain name of the server you want to join. You can find this information on the server's website or by asking the server's owner.

Click "Done" to add the server to your server list.

Once the server is added to your list, click on its name to connect to it.

If the server has any additional requirements, such as a specific version of Minecraft or a password, you'll need to enter those before you can join the server.