Automating Android tests for your Android apps is similar to automating iOS apps tests. Except for the fact that your target platform is changing, your test scripts will not undergo any change. The following diagram that shows the workflow:

Again, Appium works as a Remote WebDriver and receives the commands from your test scripts over the JSON wire protocol. These commands are passed to Google UI Automator, which comes with Android SDK, to be executed on the native app launched on a simulator or a real device. Before the commands are passed on the UI Automator, Appium translates the JSON commands into UI Automator commands that can be understood by UI Automator. This UI Automator will launch your app on the simulator or real device and start executing your test-script commands on it. After the command is executed against your app on the simulator or device, the target app sends the response to the UI Automator, which is transferred to Appium in the UI Automator response format. Appium translates the UI Automator responses into Selenium WebDriver JSON wire protocol responses and sends them back to your test script.

This is the high-level architecture that helps you understand how Appium works with Android and iOS devices to execute your test commands.