Stunt Jumps are unique places where you can launch off in a vehicle. There is usually a ramp to give you a target to aim for. Each stunt jump as a distinct start and end. If you miss the landing area, you will fail the jump.
While the vehicle is airborne, it will be under "carefree controls". Tilting forward or back will adjust the forward or back pitch while going left or right will roll the vehicle left or right. You can also affect the passage of time while performing a stunt jump. By pressing Up or Down on the Right Thumbstick you can speed up or slow down the speed of the jump. Do as you need to for adjustments.
You must then land the vehicle at a specific location with all wheels touching the ground. This helps a lot in securing a successful stunt jump. The number of stunt jumps completed can be seen on the progress scene. Each completed Stunt Jump will earn that character Driving Skill Points.
Counted Hobbies and Pastimes
To get the counted 10% toward your 100% you need to complete a minimum of 25 Stunt Jumps.
For the Show Off achievement/Trophy, you must complete all 50 Stunt Jumps