Remove the plastic layer at the top of the water decal. Place the piece of paper with the print in a container of water and take it out when you see the print come loose from the paper. Take the piece with the print and place it on the nail.
You can work the waterdecal into the nail before putting a thin layer of your product, putting the chosen piece into the nail and then using a clear product to finish the nail. After this, finish the nail with a topcoat.
You can also put the waterdecal on the nail, you do this by putting a thin layer of rubberbase on the nail, put the piece of print on the rubberbase and let it cure. Once it has hardened put another layer of rubberbase on top. Finish the nail with a topcoat.