An explicit intent specifies the component to start by name, while an implicit intent declares a general action to perform, which allows a component from another app to handle it.

The main components are Activities, Services, Broadcast Receivers, Content Providers, and Intents.

By using flexible layouts, density-independent pixels (dp), scalable assets, and defining specific resources for different screen sizes and densities in the res directory.

ANR stands for Application Not Responding. It can be prevented by performing long operations in background threads, avoiding blocking calls on the main thread, and using LruCache for loading bitmaps.

The ViewHolder pattern is used in adapters to improve performance by avoiding repeated calls to findViewById and to ensure smooth scrolling of ListView or RecyclerView.

Android uses a combination of techniques such as reference counting, garbage collection, and paging to manage memory. It also provides tools like the Memory Monitor to optimize memory usage.