A transfer sheet is actually a slide coated with an edible material and on which a graphic design is printed using edible ink. Piping meringue on the transfer sheets and the image transfers to the meringue in the heat of the oven.

You can also pipe chocolate on the sheets and the image transfers to the chocolate in the refrigerator.

You need to have a printer with edible ink to print the images on the sheets.

Sugar sheets are made mostly from sugar, combined with additional stabilizing agents to maintain their shape and flexibility. 
They are printed with a printer and edible ink. 
They are mainly used to decorate cakes, but can also be used on meringues, cupcakes, cookies and more. 
Sugar sheets should be stored in a cool, dry place, away from heat and moisture.