You duplicate your background layer in Photoshop so you have foreground and background elements then use masking to isolate the parts of the image you want to have on each layer. These layers are arranged in 3D space in After Effects and you animate the camera position. Simple as that.
If you are completely lost with these instructions you need to start with the basics of Photoshop and the Basics of AE. There is not a one click solves my problem solution. This requires careful work by hand, planning, and the right kind of shot.
The effect is sometimes called the "Kid stays in the picture effect" from the movie of the same name. The technique is far older than the move and goes back to the earliest days of film production using matte paintings, razor blades and photographs.
I hesitate to put up this link because it sounds like you are very new to Photoshop and AE if you don't have any idea how to separate elements in an image but here it is anyway.
You are correct about experience in Photoshop on layers and AE on animation. I have a simple straight flag photo with sky background. I thought I could animate the flag. Gertting photo into layers for AE is a block. COPILOT has good tutorial on AE. I will start with the basic with are better than ADOBE training DVD. Thanks for the basic info.