You can just leave the "instance variable" of the button on its properties. If you want to use a button to go to another layout I think this should be it.
Scenario: Layout 1 with Button1, Layout 2
Event sheet of Layout 1
condition: button1|on click
action: system-> go to layout -> Layout 2 (Go to Layout 2)
here is a sample of that:
dropbox.com/s/ihttjidq3b8zb1s/sample.capx