Garage doors that do not have openers usually have keyed cylinder locks much like any other entrance door. If you have difficulty locking the door, it is most likely due to the locking bars not lining up with the locking holes in the door track. The locking bars attach to a disk on the inside of the door lock and stretch across the width of the door. You can quickly fix your locks by adjusting the guides the locking bars ride on and get your door to lock.
Locate the square hole on the inside of each door track. The hole will be around the height of the second door panel from the bottom. This is where the locking bars will go through when locking the door.
Close the garage door and attempt to lock the door from the inside. Locate where the ends of the locking bars hit the track and miss the hole.
Loosen the screws that secure the locking bar guides at each end of the door panel with a 3/8-inch socket wrench. The locking bar guides are the brackets that the locking bars ride through.
Move the locking bar guides up or down as necessary until the locking bar is aligned with the hole, and tighten the retaining screws. Open the door fully, then close the door. Lock the door from the inside. Adjust the guides again if necessary.
If the key is difficult to turn, spray lubricant into the cylinder and on the inside of the lock. You can also loosen the screws securing the inside of the lock, then retighten the screws. Sometimes due to expansion and contraction of the door, the inside stem will bind. Loosening and retightening the screw will eliminate the bind.