Fold your fabric in half. Measure around your neck, loosely, or add an inch or two to the measurement. Mine was 16 inches. Mark each end.
Next, on each end, where your marks are, measure four inches, and cut.
Find the middle point between the two cuts. Measure about an inch and a half, and mark it. This makes it a lot easier to see where you should cut.
On each end, cut toward the middle mark. It should now look something like a collar.
Fold the ends in (you could iron them to make it easier) and sew each of the ends. The corners are real tricky.
Next, start sewing in the rest from the middle point.
Aaaaaand, ta-da! There is your collar! I'm sure there are other ways of fastening the ends together, like a button or a hook and eye, but I used a safety pin.