I'm a retired Microsoft Windows software engineer and haven't done anything with programming in close to 20 years.
For fun I've been working through a very popular C# programming book and I've learned a good bit about what's going on with Windows programming today.
I'm doing what I'm doing with C# after doing some Google searches, watching a few YouTube and Microsoft videos, and here I am with the book "Pro C# 7 with .NET and .NET Core" by Andrew Troelsen and Philip Japikse. I'm loving it.
There has to be a similar great book that will walk you through Android programming. Always remember, Google is your friend!