Answer 1

Download android studio, and follow tutorial about android development on android studio

Answer 2

You need to learn Java, xml, SQL and knowledge of Android API.
It could be different than writing consoles programs in Java alone.

Grab a ide for Android development like Android studio. Than you can start testing your apps.

Answer 3

Courses for Android Development...
https://digitaldefynd.com/best-android-development-course-tutorial-training/

Answer 4

Md Sahil don't be overwhelmed by the answers. If you know the basics of Java like loops, arrays, OOP, Threading, Exception handling, etc you're good to go. Go to youtube and search Android Beginner tutorials. They'll teach you a whole lot including Java syntax that are needed for Android App development. Back when I started, I understood the basics and started learning Android development immediately. The courses online taught me the basics of Android and XML and I found it pretty easy to work with.