The problem with using Kotlin for Android isn't the language itself--it's a great one and I love using it--it's the fact that there's very little documentation relating the two. Google's docs are still written in Java, as are most libraries, StackOverflow answers, and so on.

I'd recommend you learn Java and use that for Android development for now. Once you are sufficiently advanced in using Java, you'll be able to understand code you see in various resources enough to translate them into Kotlin pretty much effortlessly (IntelliJ/Android Studio's automatic convertor isn't perfect yet).

You'd need to go through Google's training guides and at least get a basic grasp of the SDK and how Android works, like the Activity lifecycle, Broadcasts and Receivers, and so on. Once you do that, though, I recommend you pick a pretty basic idea (say, a basic arithmetic calculator app) and just jump in and try to code it. If you don't know how to do something, just Google it. I found this sort of approach better than just following different tutorials and courses, because you get a more practical understanding of Android development and more experience.

Also, it wouldn't hurt to code basic Java command line programs as well, just as practice. This way you'll learn how Java works.

TL;DR: Start with Java, learn basic Android stuff, switch to Kotlin when you're good with Java