[lamida]

I also just started doing Android in my work (previously mainly doing backend development). I see that the best resource will be just the Android documentation itself [1]. I can't suggest any specific book, because book about Android get outdated very quickly. If you like an online course, Udacity offers some Android courses [2] that is made by Google. As an additional note, once you have passed the basic hello world application and understand the basic concept of simple activity, lifecycle and intent, you should explore Android Architecture Component [3] which is required if you want to write a bigger more complex application. Last, for youtube video just see Google I/O videos or any other Android conference video, once you want to dig deeper for more specific topics.

[1]: https://developer.android.com/docs

[2]: https://www.udacity.com/course/developing-android-apps-with-...

[3]: https://developer.android.com/topic/libraries/architecture