'Scroller' is just a sprite object moving slowly up the layout. Try making it visible so you can see what it does.
Y co-ordinates increase downwards, so if the Y co-ordinate is greater than something it means it's below, and less means it's above.
I think the latest version of the template uses the viewport expressions, which means it supports any window size. For example, to allow the player to move anywhere on-screen but not go off the top or bottom of the screen, use the following (but update to use the appropriate layer name):
Player: Y < ViewportTop("MyLayer")
- set player Y to ViewportTop("MyLayer")
Player: Y > ViewportBottom("MyLayer")
- set player Y to ViewportBottom("MyLayer")