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.
A garage door that has a broken spring has nothing to support its weight.
If you have a wayne dalton torquemaster system pictured below the springs will be inside a tube.
Replacing garage door springs is not a do it yourself project replacement requires special tools and techniques to prevent injury.
You will have to look up at the springs to determine if one is broken.
A garage door should not be opened until the spring is repaired.
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.
Just like car tires are rated by miles garage door springs are rated by an estimated number of cycles 1 cycle your garage door going up and down one time.