*echoes Photoshop*
Get the standard image you want, whether that's a still from your gameplay or whatever. Apply a Gaussian blur to give it that sweet depth-of-field effect and add a Text layer over the top to get whatever writing you want. You might have to install some specific fonts - try DaFont, they're amazing and the majority of their stuff is free to use.
If you don't know how to apply these effects, simply look them up on YouTube or on Google. There are so many tutorials out there that you'll have to specify what it is you're after in particular. Photoshop does a lot of stuff!
Also, play around with it in your own time. Seriously, it helps so much.
When I was completely new to the program I looked up the basics online and then just faffed around for myself.
Good luck, bro!