The Wilson 859922 Combiner/Diplexer is a coupler which allows you to either combine 800MHz/1900MHz into a single signal (or vice versa). It is most often used to combine signal from two single frequency amplifiers to be fed into a dual band antenna. It can also be used to split signal from a dual band amplifier into 800MHz and 1900MHz components. This could be used if you have two areas with people on different cellular networks, although this is rare.
The splitter has N Female connectors. Typically a 2ft LMR400 cable is used to connect the diplexer/combiner to the amplifier. Any cable length can be used, but the total cable length in the system should be kept to a minimum to minimize attenuation.
Lengths of coaxial cable can then connect the diplexer/combiner to the external (or internal) antennas.