Torsion springs store energy by coiling tightly as the door closes.
When the door is closed and at rest the torsion spring stores enormous amounts of energy and when you want the door to open the spring helps by uncoiling and releasing that energy.
Torsion springs sit against the wall over the garage door. You should never try to install or repair a torsion spring yourself because it’s very dangerous and requires the right tools and experience.
Extension springs run parallel to the tracks of the door and are typically situated between the tracks and the garage ceiling.
Extension springs store energy by extending while the door is closing and then releasing the stored energy while the door is opening.
You should not be around when extension springs snap! They can go flying and are very dangerous.
This type of spring system is not common in California.