These pocket holsters are made to stop the pistol from 'printing' on the outside of clothing.   The plain side is worn outward to hide the shape of the pistol. The contoured side is worn against the leg.
When your fingers slide into these wallet holsters, the back plate is pushed out and locks the holster into your pocket (see photo #2), and the molded socket lets the pistol slide freely out.  This holster design gives full access to the hilt and trigger of the gun as it is drawn. 
This holster is set up for the left hand, and can be used in pants or vest/jacket pockets, purses, totes, etc.  Depending on where it is carried, the holster can also be used for right hand access to the pistol, as in a right pocket or tote where the pistol shape will not be visible.