First, separate the tiles into color groups.
Take the contact paper out that you cut. If it is still curling on you, then roll it in the opposite direction and then let it unroll and do that a few times.
Cut pieces about 6 inches long and tape the sides, ensuring you meet the bottom corner and get close to the top.
First, put on your protective gloves. Then add about 2 ½ to 3 cups of the thinset mortar to a large bowl, and mix the water in.