When you place the block you'll notice your player's head will show up inside.
Anything inserted in the block (by via of hoppers, buildcraft pipes or whatever) will be inserted into your players inventory. And of course, anything pulled from it will also be pulled from your player's inventory.
The head in the center will always look in the direction of the player! Even if it's really far away
Manipulation of players inventories
You can use any head in the center
Or vanilla heads.