If the star is invisible to the eye and visible to your telescope (which you can find out by calculating the limiting magnitude of the telescope) you can only find it by its coordinates. There are two types of coordinates - equatorial (right accension and declination) and alt-azimutal (altitude and azimuth), the first being more accurate and more slowly changing. The equatorial coordinates are measured in degrees, minutes and seconds (0 to +90 in the northern; 0 to -90 in the southern hemisphere) for the declination and in hours, minutes and seconds for the right accension. There are two ways of pointing your telescope: the easier one, if it has a 'go-to' system - you just put in the coordinates of the invisible star; the harder one - you have to point it at a UMi (alpha Ursa Majoris) - Polaris and adjusting the coordinate knobs on the telescope. Then you can point at any object using the coordinate knobs. Hope this was helpful.