Decorating tips are the nozzles on the end of a pastry bag that the frosting or filling is forced through to apply it to cakes, cookies, or pastries. There are many different sizes and designs available, which will allow you to make most any type of design and allow you to do a lot of creative decorating. Some of the common tips are the round tip for line work and writing, an open star tip for borders, a closed star for flower shapes, and the leaf tip for leaves and other border designs.