Step 1: Install A11y Ally. You can find A11y Ally here on the Google Play store.
Step 2: Grant A11y Ally permissions. A11y Ally requires the "Draw over other apps" permission on Android Marshmallow and later. It must also be enabled as an accessibility service. When you first open the app, you will be guided through this set up.
Step 3: Explore the filters. A11y Ally currently supports 3 filter modes. Turn on the first one, "Highlight Issues", by tapping the switch. Once enabled, select "Accessibility Issue Playground" and observe the errors highlighted.
Step 4: Try it on your own app! After exploring the filters in the playground, try them out on your own app and see what issues you can find.