Pretty simple stuff. I can explain it in a quick little paragraph...
Here is a quick explanation of the bottom photo:
Simply find some grunge brushes, or a texture. Now copy that texture or draw over your background with it.
Then, select two colors in your background and foreground place (on the toolbar at the bottom) and on a new layer above the background layer go to Filter > Render > Clouds. Set the clouds layer to Color.
Now, make a new layer for each photo you want on the document. Paste the photos on each layer (each photo having a seperate layer). Then, grab your brush tool, click the Layer Mask button (this can also be found in Layers > Layer Mask > Reveal All). Now you have a square next to your layer with one of your photos.
At this point, position your photos (hold CTRL then click and drag the photo) to the place you want it to be on each layer.
Then, add a layer mask (same way as before) to each photo layer (not the background layer) and grab a brush, make the background color black (toolbars, the top box make it black, so now you're brushing black on a layer).
Now, click on the top layer with a photo on it, and then click on the white box next to that layer. Now with your black brush, brush outside the person so it takes out the background and now reveals the layers under the layer you're brushing on right now (should be the top most layer).
I hope I made sense, feel free to ask any questions. This method is called blending, however. Layer Masks is what you need. You might want to move the layer with the mode set to Color above all your other layers, so it colors your other layers. And then set the opacity down to about 80% or whatever looks good.
Here is a photo of how you should be set just to help you out:


The only thing I added was I copied the background layer over two photos so the photos can have the texture like the second photo in your original post some people have in that photo. So, I lowered opacity on that texture above my photo layers. Some of the people in the second photo in your original post do not have a texture, so I put those layers above the background copied texture layer.