As others have said,
the lever when in run position lets the engine operate normally. But when open, it holds the intake valve partially open to release the compression. When that's done the engine spins to high speed while cranking with the starter motor. While at high cranking speed, if the lever is suddenly closed, the engine will hopefully start. These levers were thought to be compression releases for a dead battery to allow hand cranking but Americans are too fat and out of shape so Yanmar relabeled them as 'low battery compression release levers'. That means you still need a start motor and a little juice in your battery. Any other questions?