Anytime the pitcher loses possession of the ball, while the ball is live, runners can advance. When it happens on a pitch that slips from the pitcher's hand, same answer- live ball, runners may advance.
It gets a little trickier if the ball actually rolls to the plate. Since this is still a pitch, the batter may try to hit the ball. If batted into play, it is treated the same as any other batted ball. If the batter swings and misses, it is a strike. Otherwise, a ball is added to the batter's count.
If the rolling pitch is approaching the plate, where the batter would have some reasonable chance to offer at it, and a the catcher or other fielder moves in front of the plate and fields the ball before it reaches the plate, that is obstruction (same penalty as catcher's obstruction).
Prior to delivering the pitch, the pitcher must bring the hands together. She does not have to actually place the ball into the glove. A simple touch of the hands meets the requirement of bringing the hands together.