I have a D7000, but basically the same camera justDX. You want to look under the live view focus tracking section. Sorry but you do have to read the manual if you want to use it correctly. The thing the manual doesn't tell you is full frame movie AF tracking uses contrast detection and doesn't work very well with subjects that move a lot. Canon doesn't have that feature exactly, but what they have is sort of a prefocus that works. So if your shooting something moving with Nikon you basically have to use MF if you want good results. Sort of why MF lenses are back in vogue, good old AIS lens with an aperture ring come in handy.