A garage door cable is under real tension because it's tied to a spring system, and winding or unwinding that tension wrong is how people lose fingers or get hit by a bar that lets go. This isn't a job to learn on your own driveway. If you've got a torsion spring door, the spring has to be fully unloaded before the cable comes anywhere near your hands, and on the older drum setups common in this neighborhood's housing stock, getting the winding cone seated wrong means the next person to open the door could get hurt. We'll say it plainly: this is one of the few garage door jobs where we don't walk homeowners through it over the phone, because the margin for a bad outcome is too high.