Double exposures are created in Photoshop by going to file>scripts>load files into stack. Then you rearrange your three images in to a crop of 8.5x11, make sure the crop is even all around your head. When you've done that you use the dodge tool and go around your image till around your images white. After that then you double click on both of your photo layers one at a time and turn it on screen mode so its like you turned the opacity down. When that's done you go to layer>new layer adjustment and you choose one and change it up until you like the image, then you keep adding more until you think its finished. That's how you make a double exposure and why would you want to make one maybe because they look really cool and their also really pretty. Plus most of the time when you make double exposures you can put two symbols that represent you (those would be the two photo layers).
For my two symbols I chose a waterfall and a heart-shaped flower. Why do these two things symbolize me? You my ask, well the waterfall symbolizes me because I love the water and the waterfall shown. This waterfall is a waterfall me and all my friends go on the weekend or on our free time. The flower stands for my love for nature and how its so beautiful.