First I start by choosing a psd coloring. There are thousands of free psd's available to download on deviantart. For this tutorial I'm using one of my own HERE. Then I open the psd file in photoshop, along with the photo I wish to apply it to.
Next, I select the psd coloring folder then place my curser over the coloring preview , right click and hold down on the mouse or laptop pad and drag the coloring over to the top of my original photo. If the graphic I'm working with has layers, I place my coloring folder above them, otherwise the coloring won't be visible. I might play around with the coloring settings to enhance my graphic even more. When finished I save my work as a PNG file and also a psd copy for future adjustments..
Last but not least, remember to give credit when using someone else's resources.