What is required to make Android applications?

Answer 1

An Android IDE, JDK installed. Voila.

Answer 2

Remember that you CAN run Android Studio with 2GB of RAM. Your gradle just takes anywhere from 2 to 10 minutes to build, and emulating is near impossible so you will need a physical Android device around.

Answer 3

As an extra to Hatsy Rei's answer =
Knowledge in any of the following languages : Java,Kotlin,C,C++,C#(Xamarin), JavaScript (WebView).
How to use work automaters are also essential to be known : Gradle or Maven.
Enough RAM : A developing station must have enough RAM to run the emulator and build the .apk.