just right click to add a variable (for example money)
add a spriet (for example button )
add the object 'mouse' (doubleclick and add it)
and write a code (example) :
{ on 'button' clicked - > add to money 10 }
to see the variable you can make a text and put { ' every tick - > set text 'money' }
That's it.
Now go check the tutorials !
Good luck
local-variables_t69628
https://www.scirra.com/manual/73/instance-variables
https://www.scirra.com/manual/83/variables