Sources and References for Motor Selection
In general, determining what is required to drive a machine is part of designing the machine. You start with the work being done. What is the mass of the garage door? How far must it be lifted? What is the friction force that you are working against? At what speed should the door be lifted? What is the resulting rotation speed of the shaft the the motor must turn? How does that compare with commonly available motors? What gear ratio is required between the basic mechanism and the motor?

What is the friction in the mechanism that converts lifting motion to rotation motion? Add the force required for lifting to the various friction forces. Convert the forces to torque at the motor attachment point.

If you can buy a motor with a gear attached, you can select based on the torque at that point. If you must buy or assemble a speed reduction mechanism, you need to add the torque required for that mechanism and determine the motor torque.

Some loads require additional torque for accelerating inertia. Some loads and drive mechanisms require overcoming a force or torque due to aerodynamic drag (windage).

All of this depends on the specific design parameters of the individual machine or mechanism. There may be books that tell you that aerodynamic drag and the incline grade of hills is important in selecting automotive traction motors but not garage doors, but what you really need is to learn the basics of applied mechanics and engineering problem solving. There are books and courses on those subjects.