Activities:

An activity represents a single screen with a user interface.

Acts as the entry point for interacting with the user.

Activities can be linked together to create a flow within the application.

Services:

A service is a background component that performs long-running operations without a user interface.

Examples include playing music in the background, handling network transactions, or performing file I/O.

Broadcast Receivers:

Broadcast receivers respond to system-wide broadcast announcements or events.

They enable communication between Android OS components and applications.

Commonly used to listen for events like incoming SMS, low battery, etc.

Content Providers:

Content providers manage the application's data and make it accessible to other applications.

They offer a standard interface to interact with a structured set of data, often stored in databases.

Used for data sharing between applications.

These components in harmony build up the structure and working of an android application. For instance, an application may have various activities as different views, services that perform background operations to download data, a broadcast receiver to handle certain events, and a content provider to store or distribute information.

Additionally, Android applications often use the following:

Fragments:

Fragments represent a portion of an activity.

They are often used to create flexible UI designs for larger screens, such as tablets.

Can be combined within activities to create a multi-pane UI.

Intents:

Intents are a messaging system and are used by components that require ny functionality from other components.

It helps in initiating activities, services or in sending messages normally through computers, phones or other equipment.

Explicit intents are required to identify the target component of i* elements, while implicit intents define a general action to be made.