You need to ask a specific programming question or move the post to the beginners forum.

Actually, starting game development with Android is not the best thing to do, since you've to learn Android SDK and Game Development both at the same time.

You would better get started with some games like Pong, etc. for the desktop using any language (Java preferably, since you opt for Android).

The FAQ of this forum or this post may be helpful in that case.

Once, you get enough experience, you can get started with learning Android.

Here's a good video on understanding the Android App Architecture:

For Android SDK, since you have a good experience in Java, the best place to start is probably this:

https://developer.android.com/training/index.html

Also, this free Udemy course mentioned on the above ^ page is also very helpful, in case you opt for video tutorials i.e.

https://www.udacity.com/course/developing-android-apps--ud853

You must particularly give focus on the graphics part of the tutorial (do lots of practice, maybe?), since, it will be most helpful in game development.

Then, since you'll have experience in game development with Java, and the fundamentals of Android SDK (the graphics especially), Android Game Development would follow easily.

Complete a few simple games, keep practicing and you are off!

I'm thinking of moving this to the Mobile and Console forum where many Android-related questions live, but I think I'll let it remain here in For Beginners.

To directly answer the question, you can go get Android Studio here and follow the instructions. Those are the tools you need.

Also, you can use one of the many cross-platform libraries and game engines, such as Unity, Unreal, GameMaker:Studio, GameSalad, Cocos2d-x, LibGDX, or many other tools.

However, as Tanay Karnik mentioned above, this is generally a bad choice to learn to program games. While the programming concepts are fundamentally the same, there are many additional tasks required. You need to mix together non-native libraries, use sometimes-confusing cross-compile and deploy techniques, configure and use remote debugging, and worry more about target hardware than you do on a plain desktop computer. While you can learn on mobile as your first platform, it introduces many additional barriers.

Generally the recommendation is to start simpler and follow a gentle path toward mastery. Often-recommended languages are Python and C# developed using pre-configured tools built and run on a single machine. You write that you've already mastered Java yet still don't have the core concepts to make a game. First get to the point where you can make a game on your primary computer. Once you've mastered a language and are able to make simple games, then add in the additional complexities of mobile devices.

Or you can go full 'baptism by fire' route and dive right in, that's an option some people have successfully taken.