Hello,

I hope you are doing fine, You can learn Android Development online on YouTube.There are many channels you can Subscribe on YouTube.
One of them is The Newboston or codewithharry.

Few basic steps to start android development:

1. Language you must know before starting android development is Java(core Java) as it is a major weapon in app development
2. Download Android Development Kit from here http://developer.android.com/
3. Install Sdk.
4. Open YouTube

I hope you find this information helpful. I wish you all the best for your future.

Good Luck