Idea Of HDR (High Dynamic Range)
HDR which allow Your pictures to reveal more detail in shadow and highlight than a normal shotting pictures. Thus creating a well balance exposure for the overall picture.
Both picture shows two different exposure, the higher exposure (left) reveal more detail in the inner building, however the lower exposure reveal more detail at the outside of the building. In order to have both details, You merge both of them with Photoshop (File-> automate-> Merge to HDR pro), and your result is this :
With Hdr, u have both details from two different exposure, after u have merge them, u can go wild with your images (edit it ), just have fun with it :D