***Complete noob on this subject please be patient with me***

HI, I'm trying to create a displacement map to give the illusion of a 3d pocket in the attached image, how do I go about this?

I've just got my head around texturing and feel comfotable with photoshop, now it's creating the realism in bump/specular/displacement mapping that I come to a stand still. If anyone knows of any tutorials or has time to walk me through the details of this so I (noobie) could incorporate it into a human character.

Thanks