Using old manual focus lenses with your Canon can be quite hard work, as has already been pointed out you need to focus manually and the modern viewfinder focusing screens are not designed for that, also you need to adjust the aperture manually. The normal procedure would be to focus manually at full aperture, set lens to desired aperture then press the shutter button, having to do all this can detract from the procedure of composing and taking the photograph.
Very few of the old manual focus lenses will perform as well as the better modern AF lenses, usually the best old lenses are the ones from the well known camera body manufacturers and not the ones from unheard of Japanese companies, old style zooms usually perform poorly whoever made them. Adaptors have to be made to a very tight tolerance and some cheaper ones are quite poor. Because of the design of the old Canon FD lenses any adaptor made for these has to include a correction lens and these only make the performance of the FD lens even worse,
Playing with old lenses can be fun and if you are financially stretched then it may be the only way you can afford get into other focal lengths but ultimately it will make your photography harder and probably not produce the results you are hoping for.
