You may want to spend more time going through some of the tutorials as they answer many of these questions pretty well. You can honestly add that bit of logic anywhere. If you have an event that kills the player, put it there. If not, have a condition that checks to see the state of the player and then restarts the layout. Personally in my games when I am testing I put a long sprite that extends the entire length of the layout at the bottom and have it restart layout whenever the player touches it.
That way any time the player falls off the level it restarts.