In the picture, the white spaces are the benches/ water feature that will be incorporated into the terraces. The water will flow behind the seating area creating a small boundary to the wall. On the wall you will see all of the names of the people buried in the cemetery engraved into the concrete.
The terraces give the viewer a chance to step back and view the burial area without fully engaging it. The small areas created in the terraces allow for small contemplation areas and the sound of water will give a soothing feeling to help relax emotions.
Here's a series of drawings to help you visualize this idea.