Android development

 I will start with the reference web sites before I write any details:

Android

A simple tutorial for a beginner: 

https://www.tutorialspoint.com/android/index.htm

Android API: 

https://developer.android.com/reference/packages

Get Android Studio from here:

https://developer.android.com/studio

Application Fundamentals:

https://developer.android.com/guide/components/fundamentals

Kotlin

Kotlin crash course: 

https://blog.kotlin-academy.com/8-minute-crash-course-on-kotlin-programming-language-e8a804ed3d8a

Kotlin by example:

https://play.kotlinlang.org/byExample/overview?_ga=2.6925172.73421686.1613236114-1542845850.1613236112

Kotlin programming language:

https://www.geeksforgeeks.org/kotlin-programming-language/

Installing Kotlin for mac to run apps from command prompt:

https://medium.com/beware-of-the-app/using-kotlin-from-cli-on-mac-4560b5c70604