Need help with sumps

[FWC]

So I'm looking at setting up a new tank, however a sump will be needed.

I've never used a sump before, and try as I might, they still manage to confuse me.

Notably, the tank I'm interested in is the cube in this classified add :

http://www.canreef.com/vbulletin/sho...highlight=cube


So how exactly would the sump work for this tank ?? Like that would go where ??