There isn't really a "stop" mode as such. Do you mean after starting your car (or bringing it inside to load tunes and plugging the power pack in) you don't necessarily want it to continue from where it was when it powered down?

If so, the top button will pause the unit and holding it down will put the unit into standby. Standby basically only stops the player and turns off the display. You can do everything like syncing etc while in standby.

Does that help?