First, here is a youtube review:
Fluval C3 Power Filter Review - YouTube
I just installed a C3 on my 29 gallon on Monday. It is easy to do.
Water flows from back to front as follows
1) Mechanical Frame has a Poly/Foam Pad insert to remove large debris
2) Chemical Basket - Activated carbon comes in a biobag in the the package along with the filter. Don't order refills because after the first month, you don't need carbon so you have a bazillion choices on what to put in here. I recommend filter floss + seachem purigen + 100 micron filter pad for water polishing.
3) Biological Trickle Chamber - Holds the C-nodes for biological filtration. It is covered with a thin "bio screen" media. to provide additional "trickle system" filtration. Watch the above you tube video to see it in action.
And there you have it !!
Note: The C series needs more space between the back of the aquarium and the wall than most. The C3 needs about 3 &1/4 inches. The C4 needs about 4 inches as I understand it. The aqua-tech 30-60 on my 38 gallon only takes up 3 inches and I have about 3&3/4 inxhwa of space so I can't fit a C4 or an AquaClear50 (both brands made by HAGEN) on my 38 gallon.