Corrugated plastic, plastic cardboard and plastic board are three names that all comprise the same material. Corrugated plastic is sometimes sold under the trade name of Coroplast. This material is usually made of polypropylene sheets of varying thickness arranged in long parallel cells. The overall construction comes in varying thicknesses as well. Thinner corrugated plastic sheets may be used for packaging, signage or crafting models, while thick sheets are typically reserved for larger signs or even roofing.
Lay the sheet of corrugated plastic out on a flat, hard surface. If you are concerned about scratching that surface, place a board or piece of plywood underneath the plastic.
Mark the lines where plastic is to be cut with a felt-tip pen and a straight edge.
Cut through individual layers of the corrugated plastic with a utility knife. This is the best technique when you want to cut into one side to help mould the plastic into a corner or other shape. You can also cut all the way through the plastic board with your utility knife if it's thin enough.
Make most cuts that go all the way through the plastic, especially in thick pieces of plastic board, with a band saw. Just lay the plastic cardboard out on the surface of the band saw and feed it through, following along the lines you've drawn for cutting. Use the finest-toothed blade possible on the band saw in order to achieve a clean, even cut without splinters.
If you're cutting your plastic cardboard by hand, you might consider using a PlastKut knife, which is specially shaped to cut corrugated plastic cleanly. See the resources below for more information on this specialised tool.