One of the easiest Photoshop effects is to create a double exposure. You just need to have a little knowledge about how to create Layers.
Here are the steps:
1. Decide on two images that you want to juxtapose, one on top of the other.
2. Open the two images in Photoshop. Don’t put them in browser tabs; open them in separate windows.
3. Find the Move tool. It’s the first one in the Tools palette. Click on it.
4. Drag the image in one window into the window of the other image.
5. Make the Layers palette visible by navigating to Window>Layers. You’ll see two layers, a Background Layer and Layer 1.
6. Move the Opacity sliders so the image in the background layer starts to show up juxtaposed onto of the image in Layer 1.
7. Adjust the slider until you get a result that you like.by