a), Wireless Remote Shutter Release (On camera)--- You can mount one receiver into the camera and connect it with the camera via the 2.5mm shutter connecting cable, and can remote control the camera with other receiver. You can use it to fulfill the function of Auto-Focus, Continuous shooting, Long Exposure, Half-Way Pressing, Full-way Pressing and Bulb. b), Remote Shutter Release (off Camera)--- You can use the single receiver to fulfill the function of remote shutter release after you connect it with your camera via the 2.5mm cable.
2, Flash Trigger
a), To fire the Flash Speedlite --- one receiver can fire one flash speedlite, one set of RF-603 can control 2pcs Flash Speedlite at the same time. b), To fire the Studio Strobe light --- You need to purchase an extra 6.35mm cable to fulfill this function.
3, You can use ABOVE TWO FUNCTIONS simultaneousty.
4, The RF-603 Nikon version and Canon version can be used together
If your have 2sets RF-603 but you lost one receiver for Canon version, it's no need to buy other receiver, you can use the Nikon receiver and Canon transmitter together. (Note: the hot shoe of transmitter should be compatible with the hot shoe of camera when you use them together.)