FZ18 has 18x zoom lens built in and does not require another lens to operate, but you can add a telephoto extension lens or teleconverter to it, which usually come in 1.7x, 2x or 3.2x ratios, giving you 30x, 36x or 58x zoom combined; there are also wide angle extenders
because the built in zoom lens extends outwards, most extension lenses require an extension tube to fit onto the camera; the tube has female threads for the lens on one end and male threads for the camera on the other; maybe you are missing this tube
with high zoom focusing on a small object far away, the camera receives little light energy on its sensor, and usually need a long exposure time, making it susceptible to hand shake; it need to be held steady during the shot; in bright conditions, holding the camera against the eye, because you use the viewfinder rather than lcd screen, helps to steady it, but it is safest to put the camera on a tripod
Good advice by Yuen Chung Kwong. Your Fz-18 should be bundled with an adapter tube where you can attach the hood or filters. But come to think of it, you already have an 18x optical magnification built with your camera. Unless you are a professional shutterbug, the 18x should be more than enough to cover all your basic photo needs.