I'm not familiar with either your camera, or the device in the picture, so this is going to be half-hearted advice.
Generally, there are a couple of ways you can syncronise - with the flash on your camera and with a synch lead. The compatibility of various units can be very complex and the only real standard connector is the so-called PC lead which is a small jackplug thing. You can get a string of devices attached to this and they should all fire at once.
From what I can see, the box you've shown is a power pack. Some lighting rigs are triggered by this box, and some have additional controls on the flash heads. Different brands work in different ways. When I've been working in a studio (rarely admittedly) it's just been a case of getting a long PC lead and whacking it into the control box. The control box then charges and triggers the lights. The lights have a turny power output thing on them and you set them at the level you want, get your light meter out, press the test button, meter, set your camera's aperture and shutter speed and when you shoot, it triggers the flash and it all works.
Whether your 20D has a regular PC flash socket, whether that box synchs and triggers the heads you've got or are planning to buy, whether that box has any other kind of features you need, whether it's enough power for the heads you want.... etc. it goes on and on.
Generally, I'd advise people starting out to buy a kit that they can afford, rather than trying to grub together a system from
eBay. Even within manufacturers, there can be some compatibility issues, especially when it comes to fitting brollies, softs etc. so it's wise to plan out on paper what you want, rather than going for a random box. It could be an expensive journey if you buy that and find out that it can only power one light!
Rob