How to use a neewer speedlite with my canon t2i?

Can't afford an expensive canon speedlite so I bought a neewer tt560 speedlite. I put it on the camera and turn it on, and the camera says that the external flash isn't compatible. I bought this on amazon and in the description it said that it is compatible with canon and nikon dslr's. How can I make this work?

Set flash and camera to ISO 100. If the flash has an Auto setting put it there. Set the camera to Manual mode and select the fastest flash sync shutter speed. If you don't know what it is, try 1/125s. If the flash is in Auto mode, see the recommended aperture size it indicates (at the back) and set that on the camera. If none, try f/5.6. If the flash is too bright, raise f/number a bit. If too dark, lower f/number. If you still can't get the right setting, try stepping backward to lessen flash strength or nearer to make it stronger.

I never heard of a brand called "neewer". But be aware that the voltage on flash units specifically for digital use, have a lower voltage than the flash units that were made for film cameras. I would double check to make sure the flash is designed for digital cameras.
Older flash units (designed for film cameras) can be used on digital cameras but there's product called Wein Safe-snych which must be used between the digital camera and the flash unit. Otherwise you run the risk of burning up the flash contacts in the digital cameras. The Wien Safe-synch costs about $50.00.