The lever should “lock” into the tilt position. I would leave it there. If you hit something the motor has some give, & will tilt up, hopefully saving you from serious damage. The only reason for the “Lock” position is that if running in reverse, it prevents the motor from coming up. This is not a problem unless you decide to pull a bunch of power while in reverse.
unless you have one of the last models, there is not STOP button. The owner manual says by turning the throttle all the way to idle, it will stop the motor. All it does is retard the timing to the pojnt the motor will not run. These are wonderful,msimple motors, (I currently have 4 of them), & with basic maintenance they will run another 50 years.