You'll need: fabric (at least 1/4 yard, but 1/2 yard is better), cardstock, scissors, snaps (or hook-and-eye closures). Not pictured: sewing machine, needle and thread, iron.
//1. Sketch out the shape of the collar on the cardstock. I winged it, but you may want to take some measurements to be safe. You could change the shape of the collar too! // 2. Fold your fabric over itself so you can cut two pieces at once. Pay attention to your fabric's pattern if you need to! Pin your paper collar to the fabric and cut. Leave a little room around the stencil for your seam allowance.//
//3. You should end up with this shape. Make another one for the other side of your collar. //4. Pin your two pieces of fabric with the right sides facing each other. Make sure you keep the right pieces together, you need them to line up as best as they can.//
//5. Starting at one corner, begin sewing around the edge, using your sewing machine's foot as a guide. //6. Sew almost all the way back to where you started, but stop about an inch before. Use the little opening you left to turn your tube inside out. You may need to use a pencil to get the corners pointy. Do this for both halves of your collar.
//7. Iron both pieces flat. Hand sew the two halves together at the center. //8. Sew a snap (or hook-and-eye-) at the back of the collar (the top corners of your collar). That's it!