It's a kit that's meant to be used against a backdrop

The build does look pretty straightforward, but they really didn't explain it too well.  This kit is meant to be placed along the back of your layout with either both side walls attached to one front wall, or the base and roof cut into a triangle shape and then those are assembled with either the left side and front glued together or the right side and front glued together.  That's what they meant by a "left-hand building" or a "right-hand building".

Walthers' instructions historically have been barely adequate for someone who hasn't already figured out how the kit goes together by looking at photos of the assembled kits.

This particular kit was based on the Walthers Part # 933-3026 Red Wing Milling kit, and is made up of the back wall of the Red Wing kit and 2 side walls that are half the width of the side walls in the Red Wing kit.  I haven't been able to track down a photo of the sprues included with your particular kit, but you may have an extra 'front' wall.

Hope this helps explain things. If you can, let us know how it turned out.

Janet N.