Russ,
The router sends and recieves signals. So it acts as a transciever which is a radio which can transmit and also recieve signals.
The router is designed to operate best in a range of frequencies. The antenna is also deisgned for the same range of frequencies
and can enhance both an incoming signal and outgoing signal and that is expressed in terms of its gain. 3db doubles or reduces
the signal power. By "deisgned for", the antenna can take those electrical signals in a certain range of frequencies and enhance them and same goes for the router. The router has internal circuitry to accept and reject signals not in its range of frequencies
so it filters outs the signals.
So if you point the antenna at the cell tower you'll get the best transmissioin and recieve to and from the routers antenna.
Just like what you do for an old TV that uses an antenna. Comunication towers can have a beam width angle of only 1 degree.
Thus antennas have transmit recieve and gain, more sensitivity to certain signals, and can be more directional and that depends the type of antenna.
The signal from the router has a very low power level, mw ( milli watts ). The line connecting the router to the antenna
will cause signal loss. Since you don't have much power you want to minimise that loss and as such you want to use an
appropriate cable for the range of frequencies it will transmit. The antenna will then increase that signal to the cell tower.
The less abstruction in the path of the signal the better the electrical wave can travel. So mount the antenna on your pole
above ground with the cable from the antenna to the router inside. The PC wireless USB adapter can then be used by any computer to communicate with the router. Another way is to run cable to the router from the pc.
Tried to keep this very generic and not get techie about anything.
Hope this helps,
BTW, Merry Christmas

RICH