When should you apply hand brakes?

After parking your vehicle

Using your handbrakes ensures that the car's weight isn't resting on the parking pawl.

After parking your vehicle

Using your handbrakes ensures that the car's weight isn't resting on the parking pawl.

During an Emergency

In case of emergency, if your footbrake doesn't work, pull up your handbrakes! 

when stopping your vehicle from rolling

You might be in stop-start traffic while driving uphill. At that time, your handbrakes help the car from rolling backward

While waiting at an intersection

Use your handbrake to avoid accidents at an intersection. Having your foot at your brakes while waiting at an intersection might lead you to hit the car in front of you.