How does the mechanism of paid Android applications work?

Question

Android

Good afternoon ! I saw several types of paid applications in the "Google Market":
1) There is a version of Light and Pro (separately), that is, there is no money to download "Light", if you want "Pro", then you pay and download Pro!
2) The application is free with the ability to buy additional functions, and when you buy these additional functions, they open in this application (which interests me).
- That is, how to do (what to read about it\examples) to create something like this:
An application (by the type of reference book) a person reads the reference book, everything is ok, but for example, comments on some texts are not available and what would they be available (or open ) you need to buy the "Pro" version, the person pays and it all opens! - how to do it, what to read, can someone have examples on the gita? Thanks ...
PS: I may not know a lot of things and perhaps I didn’t ask the question correctly, but you should understand the essence, I apologize in advance if I didn’t quite adequately ask the question ...

Answer 1

This is called IAP (In-App Purchase). Start reading here - https://developer.android.com/distribute/best-prac...