To access the Drives section of the app select My Car at the bottom of the app, then tap Drives. From there, tap Turn On Permissions
Each drive can be selected individually to show more detail such as time spent, and any hard brakes, accelerations, or speeding that may have adversely affected your fuel efficiency on a given drive.
GasBuddy is able to detect speeding, braking, and acceleration through a combination of geo-coordinates, gyroscope, and accelerometer information that your phone already tracks.
Note: A drive is detected after approximately 2 minutes of constant motion and stops detecting after approximately 2 minutes of stillness. This accommodates for things like traffic lights which may cause you to stop for a while, but not be the end of your drive.