You'll need an overflow or a siphon box of some sort to drain water out of your display tank and then drain it into the sump system in the stand below. You'll need a return pump to move water from the sump back to the display tank. You'll want one with a flow output that's close to the draining capacity of the overflow box (the manufacturer should sell the overflows based on GPH of flow) Remember to take head loss of the return pump into account. Feel free to post back here with the system you're thinking of and myself and others will give you feed back
As far as what to run as a sump, you could look at making one yourself if you're handy, or you can buy many different types of pre made sumps. They're fairly simple really, don't let them intimidate you.
To get the general idea of a sump, simply draw a rectangle on a piece of paper and divide it into three sections. On section is the drain chamber, where water drained from the display tank will enter the sump. The middle section is usually a refugium, where you can grow some macroalgae as well as culture 'pods for your tank. This can also be a place where you can place critters from your display tank that need a time out (predatory crabs for example). People actually have started a trend of 'display' refugiums where they grow all kinds of cool critters - but that is neither here nor there. The third and final section of the sump is normally where the skimmer is run, and where water is returned from the sump to the display tank via the main system pump described above.
You can find all kinds of plans for sump layouts both on this site and using google. You can also feel free to draw something up and post it here, and members will give you feedback. If you'd like I can snap some photos of my setup when I get back into town next week.
