First, tap into Drive and aim BB-8 but turning the model Droid on your screen and spinning BB-8 until its blue tail light is pointed toward you. This can be done at any point during driving to keep your droid properly oriented.
Slide your finger on the driving pad to guide your Droid. BB-8 will go wherever you point and hold, and even react to collisions. Tap the button to the right of BB-8's aiming model to try different animations of BB-8’s personality. Tap the right arrow in the top right corner of the driving screen to adjust BB-8's speed setting.