After connecting to BB-9E via the Star Wars Droids App by Sphero, you will automatically begin at the drive screen. Set the aim by dragging the BB-9E on-screen to rotate the physical Droid around.
When the physical BB-9E is facing away from you, and the blue tail light is visible, tap the Drive icon and a diving joystick should show up. Press and drag from the center of the joystick driving pad to the edge of the driving pad to get him to move. Move it all the way to the edge of the driving pad for top speed. When releasing your finger off the screen, place it anywhere within the driving area of the screen to regenerate the driving joystick to drive again.