Are you asking what the difference between
Pics stolen from http://www.triggersys.com
, I own a few of these products so they were first on my mind.
If so the first one is a plain old sump, just a place for water to flow into a skimmer and then return to the tank. The areas are separated with bubble traps and a separate area for the pump. This will help regulate the depth of the water in the skimmer area so the skimmer works it's best.
The second image is of a fancy sump/fuge combo, it is the picture of the sump I have, and am very happy with. The water is moved first into a foam/chemical tray for a pre-mechanical cleaning, in this area you could lay some foam, or a sock full of carbon, phos media or whatever. The tray pulls out for quick cleanings. The space under that is for "bio-balls", the pre-filter is meant to keep them clean so they don't become the waste magnets we all talk about, I instead have mine full of live rock rubble. From there it overflows into a bubble trap/ height regulator for the skimmer chamber, this keeps the water at 6". It then makes a 90 degree bend and through another set of bubble traps into a pump chamber. From the pump I've TEE'd off a line that goes to the last end chamber, a 10g refugium, this is regulated for about a 12" depth which overflows through WEIR teeth back into the skimmer chamber.
I've seen people add bubble traps in the middle of long refugiums before just to make sure the water gets mixed up. You wouldn't want it so that the incoming water just flows over old stagnant water.