they are a one time use...basically you just coat it with chocolate and then you can wrap it around your cake and once hard you peel back the acetate and it leaves the design on the chocolate.
You can also put it on candies, cookies, etc. Any surface that you add fresh melted chocolate too and then let it harden and peel away.
Here is a cake I did where I took a plain sheet of acetate and drew the flowers on with melted pink chocolate and let them dry and then added the milk chocolate and then wrapped around the cake, popped the whole thing in the freezer for 2 minutes and peeled away the acetate. Very fun.
Would be cool to make abstract squiggles and lines and such too on your own.....and much cheaper than the premade transfers (although not as pretty lol)