My key does not insert or withdraw easily or it has difficulty turning.
First spray the lock with light penetrating oil (such as WD-40). This oil can be found at most hardware stores, but can even be found at some drug stores and supermarkets. Don't be afraid to spray too much, but have a paper towel handy to pick up the excess. Spray the oil into the keyhole and onto the bolt mechanism. Move the bolt in and out to allow the oil to penetrate into the lock. Do not take the lock apart if you are not confident you can put it back together.

The lock doesn't lock and unlock smoothly.
After you have tried the above solution, check to see it the lock operates smoothly with the door open. If it does, your problem is not in the lock, but rather in the alignment of the door and frame. Look for obstructions at the threshold and in the door jamb. Also check the door and frame for twists and warps. The door should completely rest against the door stop and stay there. If the door rests at the stop at the top or bottom only then the door or frame is twisted. If the door springs open then the hinges are probably binding. If you have weatherstrip on the door, it could be obstructing the path of the door. Keep in mind, wooden doors and frames will warp and swell with temperature and humidity, and metal doors and frames will twist and rust with age.

I have lost the keys to my file cabinet.
Most file cabinet locks have a code number on the face of the lock. With that number and the brand name of the cabinet manufacturer, a locksmith can make a key be code for you which you can pick up. This can not always be done, but if it can it will save you about forty dollars. Expect to pay ten to twenty-five dollars for the key by code.

I have lost my car keys.
Sometimes a key code is available. You will only have access to this code if you are the original buyer of the car. This code is typically written on the original bill of sale which you may have or the car dealership may have. Rarely, these codes are written on the cover of the owner's manual. So check there as well. A key by code can save you money over having a key fitted to the car on-site. Expect to pay from fifteen to fifty dollars for a key by code.