Basically, PSD is a coloring. There are many amazing PSDs out there, which is great for people like me who are not good at coloring their stuff.
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I'm sure that a video tutorial is much better than anything L could write here.
Here are some PSDs L like, all from Deviantart:
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In case toi don't have Photoshop, toi can download it link

Now that toi have Photoshop, we can get started.
First toi need to click File--->New---> width 800, height 100 pixels. Then toi click Ok and toi have a background.

Now toi click File--->Open and toi select a photo toi want to open. Then toi crop and resize it. I usually choose 110 ou 120 height. Now right click on little window and déplacer to new window. Now your image is in new window and toi need to drag it to your banner. Then toi use a little Arrow from the panel on the left and déplacer your image where toi want it.

You do...