About

An activity is a plain Java class representing a single screen (known also as a presentation layer).

Every Activity is invoked by an Intent, regardless of how the user navigated there. You can get the Intent that started your activity by calling getIntent() and retrieve the data contained within the intent.

Articles Related

Priority

From High to Low:

• Active activities
• Visible Activities
• Background Activities

See activity lifecycle to understand the activity type. (onCreate, ….)

Documentation / Reference

• Activity - Guide
• Activity - API
• Getting Started - Starting Another Activity