Except for repair of the motor and spring, most garage door fixes can be done without a manual or professional help. The level of complexity and process of a repair depends on the nature of the problem. The motor, track and rollers are common culprits of garage door issues.
Garage doors use a high-tension spring and motor to raise and lower a tracked door. It is important to annually clean and lubricate the track and rollers to keep the sliding motion smooth.
Garage door springs are under high stress and are very dangerous. Any repair or adjustment to the spring should be done by a professional. If not using a professional for spring work, take caution and ensure the spring is relaxed with the door up before performing any maintenance.