Product Showcase - Interior

The bottom shows four feet with rubber padding. The removable dust filter to the left sits under the PSU and can be pulled out to clean.

The H500P has shield plating (metal) that you use to hide the HDDs and PSU in the lower segment. Your PSU is separated in that lower left compartment. Air will be drawn in from the front based fan intakes. Graphics cards can be any size really. Under the right side lower shield sits a drive cage. 

So on this photo I removed that right side covering panel, this now opens up the drive cages. To access the HDD trays you will need to remove four or so screws at the front and back side. You can then lift out that shielding. 
 

 
HDDs are easily seated and sit in rubberised mounts. Cooler Master allows you to install just two HDDs as well as two SSDs. You can pop in the HDD and slide that inwards and secure it.

At the inside top you can see plenty of clearance / space for cooling, you can house a triple rad there for liquid cooling, you have roughly 55mm clearance for the rad and fans.