I have just acquired a pair of Sharp stereo speakers that have an inbuilt sub-woofer. Each speaker has a separate set of connecting wires for the sub-woofer. Am I supposed to join the wires (positive to positive etc) and insert them into the same hole in the back of the stereo or should the sub-woofer wires be plugged into a separate hole. Do these speakers require a specific amplifier that has separate connections for normal speakers from the sub-woofers?

The separate set of connecting wires for the sub-woofer indicates that another signal is required than the one for "normal" speakers.

Often real sub-woofer speakers are powered from a separate amplifier.
Otherwise you use a filter to separate middle to high from low frequency output signals.

Note that for sub-woofer wiring you should use extra thick diameter wires to reduce cable losses to a minimum.

Success !

:)