It is the first time I've used this flash and have no idea how to work it. Even though it seems to fire, my pictures are dark, as if it hasn't fired.
I think you're out of luck at the moment...unless you read Chinese (all the listings say that the English manual is "coming soon" and the flash was only released in late May 2014). Flash Havoc reports that the flash still requires considerable "refinement" (read: needs fixes), and that they don't recommend purchasing it yet. There are reasons not to cheap out too much when getting your first flash. Most TTL-capable flashes cost about twice as much as the X-650 (i.e., ~$120 vs. ~$60).
Looking at a picture of the back of the X-650, the Mode button, and the control wheel are likely to be your main controls for the flash, with the LCD screen labels changing for the buttons, as you navigate around. You're liable to have at least two modes: TTL and Manual. I'd recommend putting your camera in M mode, setting it to iso 400, f/4, and 1/200s, and then on the flash pushing the Mode button until you are in Manual (M) mode, dialing it up to full (1/1) power, and if the flash doesn't fire in sync and show in the image, then return the unit as a bad one.
If you are shooting with the camera in Av/Tv mode, try switching to P mode. In Av/Tv modes, Canon cameras assume you want fill flash. If you are shooting in low light, the behavior won't be what you expect. You can set a custom function for flash with Av to change it to be more like P&S pop-up flash behavior, or shoot in P mode. But if you really want to control the flash, you should use the camera in M mode, and learn about balancing the flash against the ambient.
I would highly recommend that before you start learning flash that you be comfortable shooting in M mode, and are thoroughly conversant with the exposure triangle.