How to do a definite click?

Hey so I was wondering how you click a button no matter where it is on the screen... Here's an example...


I want to click the button "I can't sign in" -- It could be done by mouse clicking on coordinates but I want to to press the button no matter where it is on your monitor(s). I'm not sure what the proper terminology is... hooks?

I'd like to see how to do it in C/C#/Java or any language just to get a basis

bring steam to top and use tab to reach button