How to sell books through a mobile application?

Question

Books

Hello. Guys such a question.
I see there are applications for reading books on iPhone such as Ai Reader, MyBooks, etc.
The question is where do they get these books from? And how do they sell them without copyright infringement.
I just have an idea to do something like this, but in this matter I don’t understand anything at all.

Answer 1

Publishers/authors/rightholders enter into distribution agreements. Books appear on websites and apps.
Many applications combine owner/arrangements. That is, the contract is concluded alone, and the book quietly appears on several platforms.

Answer 2

Alternatively, enter into agreements with publishers