The video below shows how to make a snuffle mat. The rubber mat used in the video is approximately 12x12 inches. You can use any similar kind of mat, as long as it has plenty of holes to tie the fleece strips through.
To teach your dog to use the snuffle mat, simply spread some dry treats or kibble throughout the mat. Start out with several pieces of food sprinkled on the top of the mat. Once they get better at finding the food, you can make the game more challenging by hiding fewer treats and burying the food deeper in the mat.