Because it’s either not there or it’s not clear (I sure as heck don’t see it) in the documentation, here’s what the red and white bars mean on the built-in digital watch faces for the Garmin Fënix 3 / 3 HR:
White Bar: Depending on the watch face and additional data display as selected by the user, this is most likely an empty arc (curved bar) on the left side of the face or an empty straight bar at the top or bottom of the face. It tracks your steps goal; the closer you are to your defined goal, the more filed this arc or bar becomes. At goal, it becomes completely filled with white.
Red Bar: As with the white bar above, the exact positioning and shape will be dependant upon user settings. In any case, however, it represents the amount of movement necessary to clear a move alert. The more you move, the more this bar will fill until it becomes completely full – at which point the bar will disappear until it’s time to move again.