Count users whom press the buttin (go on screen) in Appplication

[sbdar...@gmail.com]

I want to count users whom press the buttin (go on screen) in my Android/iOS Appplication.

So i set up ga:users as metrics, ga:date as dimension, but i have no idea how to set up segments. I have name of the button (screen), for example: openAccountWaitForCall_btn. Could anyone help me to define segments?

Thanks in advance