In case tu don't have Photoshop, tu can download it link

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

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

You do...

PNG is a strategically cropped layer. tu can use it for your icons, banners, misceláneo fan art... tu can make your own PNG o download one.
link

You drag PNG files same way tu do with link

Here are some PNGs, all from Deviantart:
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link

I didn't test all of these so sorry if some are not very good.