i=0 ;makes a variable
Gui, Add, Text, vP x0 y0, The value of i is %i% ;the command v is to make a variable in the text so you can control it
Gui, Show ;Show the gui
i++ ;i+1
Sleep, 500 ;Wait a half second
GuiControl,, P, The value of i is %i% Control the variable P and set it to the new value of i