Walls are used to make the limits of Zones or to block off certain areas.
The log wall is the only wall that can be built without a workstation. It is basic, and so breaks after about 2 days. Requirements: Wood.
The wooden wall does not decay. It is the 2nd wall possible to build. Requirements: Carpenter's Bench Wood, Wood.
The Stone wall does not decay. It is the last possible wall to make. Requirements: Mason's Bench, Stone, Stone.