i didn't understand this method().method2()

Question

R.layout.main i didn't understand the two dot notion.. i knew only calling var/method with single dot pls explain m().m2()

Answer 1

The method probably returns an object, which has itsmown method method2

Answer 2

R is namespace for every Resource in your app,
layout holds every .xml style file,
main is just your layout which you've created. You can just read it like: from resources choose layout, and from layouts choose "main".

Btw. In Java it's common practice to use Builder class and they do use a lot of dots :D