How to track the processing of methods and clicks?

Question

Android

Good afternoon. Let's say there is a button in the application, when you click on it, a new Activity opens, and then you need to enter a number. How to keep track of which method is called, where the variable is passed, etc.

Well, i.e. approximately *clicked on the button*
calling newActivity()
then entered a number, calling another method, writing to it, etc.

Answer 1

did you even try to find it? this is one of the first topics, there are several ways to do it. And you don't have to track anything.
here, hold on, the variant https://startandroid.ru/ru/ was googled for you

Answer 2

If you have the source code, then obviously by reading the code.
If you are talking about someone else's compiled application, then it's not clear why you need it. But in any case, you can try to decompile it (not the fact that you will succeed) and, again, read the code.
There is no other magic, as far as I know.