With this tutorial you can learn how to blend layers together, creating cool backgrounds and other graphics for any time and place ;) Note that in this tutorial I will give an example with 2 pictures identical in size, but they don't have to be in order for this to work, they can be any number of different sizes and shapes ;)
I will start with the basic 2 mini-pictures of rose below...
Open up PS and the first image you wish to blend. Now open your second image and select it, copy it and go to the first image and paste it into it - a new layer should appear above your first image.
Next, go to Layer > Layer Style > Blending Options.
A window should appear looking very much like the one below. Under general blending, you can choose your blending mode from various cool effects such as dissolve and Soft or Hard Light, fiddle with the opacity for a little bit until you're satisfied with your result, then click OK.
After that, just save your creation or add any other effects you wish, and you're done, congratulations =D!