What is drawable folders?
A drawable resource is a general concept for a graphic which can be drawn. The simplest cases is a graphical file which would be represented in Android via a BitmapDrawable class.
Typically you would store bitmaps for different resolutions in the dpi, dpi, xhdpi, xxhdpi subfolders of res/drawable.
Android system selects the correct one automatically based on the device configuration. If you do not provide
bitmaps for all supported resolutions, the Android system scales the closest fit up or down. This is typically
undesired as the bitmap might get blurry.
What is mipmap folders?
The mipmap folders are for placing your app/launcher icons (which are shown on the homescreen) in only. Any other drawable assets you use should be placed in the relevant drawable folders as before.
What is the difference between Serializable and Parcelable?
Serializable is an standard java api which uses reflection to achieve the job. It is little slower and use more objects for garbage.
Parcelable is an android api. It is optimized for android and it is faster. It uses less objects for garbage.
What is ProGuard?
Proguard is free class file shrinker, optimizer and obfuscator. It detects and remove unused modifiers, methods. It optimize the bytecode and remove unused methods. It renames lengthier method name to smaller method.