Wire Fencing Kits are used with a Toolbox to create a barrier that blocks other players. They can commonly found in industrial buildings. They can also be removed with a Toolbox by aiming at one of the poles. If placed inside buildings, the barbed wire will go halfway into the ground of the building, making it possible to vault over it. No matter where it's placed, zombies can still go right through it, making wire fences only useful against other survivors. You do not take damage for running into it.
The most common place to find wire fences is blocking off buildings in large cities. Usually, the only way to get past it to get into the building is by using a Toolbox to remove the wire. This is done by by finding the wooden stands of the wire and scrolling there and clicking "Remove wire".