I recommend working through the beginner and advanced programming for Android tutorials on Udacity, both are free:
https://www.udacity.com/course/developing-android-apps-with-...
https://www.udacity.com/course/advanced-android-with-kotlin-...
That gives you a solid start to look into more details and do some codelabs on
https://codelabs.developers.google.com/?cat=Android
or watch a series about a certain topic on Youtube. I really like the Coding In Flow channel: