Canon DSLR's have ETTL flash which means they emit a preflash that is used for metering followed by a real flash that takes the picture. Slave flashes that trip when they see a flash will go off when they see the preflash and not recycle fast enough to fire again when the shutter opens so you see the flash fire but there is no exposure for the image. To fix this some slave flashes (I believe including your model
?) offer a 'delay' mode which causes the flash to go off with the second flash rather than the first. Some do this by counting flashes (ignoring the first) while others just delay the flash enough to give the shutter time to open. This works if the delay time is right for the camera being used or is adjustable. Look on the flash and see if there is a switch for a second mode (I do not know how it will be marked) and try the delay setting. You will know you are there when you can take a picture of the flash unit and see it firing in the picture but not through the lens. Sometimes this delay feature will require a slower shutter speed than the regular flash maximum (1/250) so you may have to try 1/60 or so to get it to work. Since the flash is not ETTL, you will have to figure the exposure (trial and error) and set the f/stop to get what you want. The flash should fire (manual exposure) from the hot shoe unless it is broken (a possibility). Note the person asking the question linked by nrottley above was getting flash. I suspect that problem was improved with the answer given there to try the S2 setting.
This really is a hard way to get a flash for the camera. I would suggest buying a compatible unit until you are comfortable enough with the camera to experiment.