GetScreenHeight() returns the value in pixels of the current screen/game window height.
Abort("This game takes up " + GetScreenHeight() + " vertical pixels of your screen.\n")
Aborts Sphere with the message of how high the horizontal resolution of the game is.
var white = CreateColor(255,255,255); Rectangle(0, 0, 25, GetScreenHeight(), white);
This draws a white rectangle over the left part of the screen, in full height and 25 pixels width.
If you don't configure your game, the screen height is 240 by default.