As gary said they only work well on some lenses and even before that they will only attach to certain lenses as well.
Generally any crop sensor only lenses will not fit teleconverters, also its a general rule that low end budget lenses will not fit teleconveters. Note that sometimes a 3rd party option like a sigma teleconverter will fit a lens which is not rated as being teleconverter compatable.
Generally I would say a good 1.4teleconverter is a good choice - offering a good increase to focal length and only losing one stop of light as well as not affecting image quality too much. However they are best kept to prime lenses - in the zoom department the 70-200mm lenses tend to be of high enough quality to take a 1.4 teleconverter - I don't know about the 55-200mm that you have though.
A 2*teleconverter is a much more tricky beast and really is only for prime lenses - on zooms it can work decently for websized images though fullsize things will take a noticable hit in the image quality area - also it reduces 2 stops of light as well.