Sure...
When creating a CAD mat, there's a couple important things to keep in mind while you're designing. The first one is making sure the design ends up as we like to call here a closed "circuit", where all the end points of line segments connect so that the software can make the appropriate calibration adjustment (overcuts and backups).
The second consideration is making sure that the points of connection are tangent if you do not intend for the knife to pick-up and replunge at a particular location. You'll see this sometimes when you have several arcs connected in series.
So keeping those items in mind, simply draw the shape you want to see. OK, so it may not be that simple at first. Back when I was a framer, I got some graphed tracing paper so I could plot out my points by hand and then would manually enter those plots into the CAD software. It's tedious but effective. We do ship CAD with an add-on from Corel called "OCR Trace" which is a raster-to-vector conversion tool (let's you scan in a picture as line art and approimates it to mathmatical vector informaiton). It takes some of the drudgery out but still involves a bit of clean up work.
The CAD we use, Visual CADD, also comes with many neat tools built in for scaling, trimming, offsetting (very useful for multi-layer mats), and rotating. Explaining how these tools work though is beyond the scope of this reply...
Finally, once you're done designing, we ship another custom tool called PathTrace that runs from within Visual CADD. PT allows you to easily pick the starting plunge on each circuit and the type of bevel you want to cut with. From there you can save it or launch the Wizard software straight to the cut preview screen and cut your design. PT will also inform you if there's some circuits not completely closed and is smart enough to try and close it for you as well.
As Mike said, we also have a full manual and tutorials available on how to complete this process.
Any specific questions?