>>2626757He might be referring to teleconverters, which are not better than an actual longer lens in most cases, although they can produce some pretty great results. They increase the focal length of your lens at the expense of your largest maximum aperture and some image quality. And possibly autofocusing ability.
Extension tubes don't increase the focal length of your lens, they let you get closer than your lens would normally allow, so you can get better magnification. It's usually for macro stuff.
