At a wild guess (due to lack of info), you're trying to lock on to an ILS approach, and are wondering how. Read up on ILS & NAV & Glideslopes. Basically, you're going to tune your Nav1 radio to the runway's ILS frequency, use the Nav Source knob to select Nav 1 (not FMS), press NAV & APPR, the approach the runway until you get a lock - maybe about 10nm out. The X-Plane manual has a section on ILS navigation and a quick Google turned up excellent tutorial results. The CRJ tutorial has some instructions starting about page 46 - although you would be well advised to start at the beginning.