What you can't see in the pictures is a small hole on the side of it that you insert your dip tube through. Also there are 2 sizes of holes..finer holes behind the shield in the photos. At the end of your boil you vigorously whirlpool your wort. This causes hops to "volcano" towards the middle...
I have 7 in stock right now if anyone would like me to ship them one. I can also explain how they work.
brian at greatfermentations.com
www.greatfermentations.com or
http://www.greatfermentations.com/Blichmann-HopBlocker/products/1190/