First do not try to lift the door by hand or using the opener as you can hurt yourself lifting a heavy garage door by hand and burn out the opener using it to try to open a door with a broken spring.
Broken torsion spring garage door.
This video will show you how to open a garage door if one of the torsion spring is broken.
This video will show you how to open a garage door if one of the torsion spring is broken.
A garage door that has a broken spring has nothing to support its weight.
Replacing garage door springs is not a do it yourself project replacement requires special tools and techniques to prevent injury.
A garage door should not be opened until the spring is repaired.
The size of the door and the type of spring system determines how difficult opening the door will be.
You will have to look up at the springs to determine if one is broken.
If your garage door has two torsion springs the second spring will keep the cables tight and on the drums.