It depends on what kind of car you have!
This may sound like a dumb question, but are you sure you have the right key? If you are, there are a couple of option. If that key doesn't work in any of the doors, the key may just be worn. It may be a poor copy, or just been used too much.
A competent locksmith will be able to visually decode the key and "code cut" a factory original bringing back to how it is supposed to be. This will likely solve your problem.
If it's just that one lock that is a problem, there are a couple things to try. First, flush it out with WD-40 to try to get any dirt that has possibly built up in there cleaned up. Run the key in and out several times, and try to turn it. Be careful not to force anything.
If the lock will still not turn and you have cleaned it the best you can and made a code cut key (if you needed a code cut key here in Fort Collins it would only cost $10 to $20), there might be a problem with the lock, for example a bent wafer (wafers are the tumblers that "read" the key). The door panel will probably have to be removed and the lock taken out and serviced by a locksmith. Good luck!
Source:
http://www.locksafesystems.com
Take your key and stick it into the lock on the door and turn.
Stick the key in the door lock and turn.
The power locks can only be engaged from the driver's door. You press down on the door lock on the driver's door and it will lock all the doors. Or you turn the key in the lock to the right in the door lock of the driver's door and it will lock all of the doors.
The answer is a key
door, doom, loom, look, lock
Insert key in the door lock and turn to unlock the door.
put in the key turn it right and pull out :) !
usually you just stick the key in the door and turn the key as if to lock it. try both the driver and passenger doors.
The door does not lock with the "door lock" button from the inside to prevent locking your key inside of the car. Simply turn the key in the door when you close it to lock all the doors.
turn your driver door lock with your key
Close the blinds, lock the door, and turn off the phone.
Remove the inside door panel. Remove the door lock linkage. Remove the door lock barrel retaining ring. Reverse the process to install the new door lock.