The co-founder of BridgingApps, Sami Rahman, has created a course on Udemy that will teach you about the the accessibility features on Android devices. This course is FREE! It covers:

1. Vision Features

2. Auditory Features 

3. Physical and Fine Motor Features

4. Language Features

If you would be interested in this course, it can be found here: https://www.udemy.com/accessibility-features-on-android/