When using an adapted manual-focus lens on a Canon dSLR, you have to use either the M or Av mode on the camera. No other modes work properly, because the camera cannot tell the lens to change the aperture setting.

**In M mode, the exposure compensation scale at the bottom of the viewfinder now acts as your light meter.**  The 'needle' does not automatically get set to "0" as it would in Av/Tv/P/Auto.  You have to put the needle there manually using the aperture ring on the lens, or adjusting your iso and shutter speed on the camera body. "0" may not be 100% correct, but it's where your camera would have put the exposure in one of the automatic modes, and should usually be in the ballpark.

You also have to focus using the focus ring on the lens, and it may be difficult to judge accurate focus once the lens stops down, because in order to get accurate metering, the camera *should* be stopping down the lens to measure the amount of light coming in.  You may want to set the lens to wide open and focus before you adjust the exposure settings.  

If the lens adapter ring you have is chipped so that it can report some EXIF, and give you the autofocus confirmation (i.e., the green dot lights up in the viewfinder when focus is achieved), you may be able to use that as well. But chips vary. I had one once that screwed up the metering in the camera by faking that I had a lens that would be wide open for metering and stopped down for the actual exposure, and whatever I had set on the lens had to be compensated for on the meter (i.e., if I shot with an f/2.8 lens, and I wanted to stop it down to f/8 for shot, and I'd set f/8 on the lens, I had to make sure the meter showed me I was -3EV). I've had others that worked just fine with stop-down metering.

My recommendation, if all this is too confusing, is to start by shooting in M mode with an EF-S lens, so you get conversant with how it's all supposed to work and what the individual settings do to an image and to exposure. (Bryan Peterson's *Understanding Exposure* is also a good reference for this). And once that's all sussed out, try again with the manual lens.