While some cars and trucks have mud flaps to prevent debris from getting into the underbelly, others are equipped with fender liners. They are used to protect the front wheel wells from rock chips and losing their finish.
Liners are often factory-installed by the manufacturer in all wheel wells, front and back, but certain models may only have liners in the front wells. Since the liners are installed to deflect debris that gets kicked up by tired on the road, they may need to be replaced from time to time.
The liner is often specific to the make, model and year of the vehicle, and the type of engine can come into play as well. When it comes time to remove the old fender liner and install a new one, you will need a screwdriver, unless the liner is attached by snaps.
The first step is to remove the old liner, and to make it more accessible, you should turn the steering wheel all the way in one direction. Once you've removed the reachable screws or clips, you will need to turn the wheel in the opposite direction so you can undo the remaining fasteners. Then you should be able to remove the old liner easily.
Slide the new liner into place and align it with the mounting holes to make sure everything fits just right, and then replace the screws or clips.