If you connect a flash via a proper sync cord to your camera (regardless of the camera), that flash will fire when the photo is taken.
Additional flashes have optical slave eyes built into them. These optical triggers will sense the first flash going off, and fire themselves. There is not enough delay between the two flashes firing to affect the image. However, this does require line of sight, and no outside source of pulsing light (i.e. no other flash photography)
Secondly, you can connect the transmitter to the camera (you may need an adapter, depending on the transmitter and camera in question), and receivers to each of the lights. When the camera fires, so will the remotes, and in turn, so will the flash units.
You can also use a network of wires an splitters to hardwire all of them together, but that is cumbersome, at best. Here is an adapter that can connect all three cords to your camera:
http://www.paulcbuff.com/ss1.php