He would have led about 16 soldiers - a corporal and 15 privates - maintaining communications between Battalion HQ and the battalion's four Infantry companies.
Communication methods would have been telephone (possible at Anzac, but not in mobile operations in WW1), morse code semaphore (flag signals), heliograph (mirrors+ sunlight), runners and perhaps lamps. Telephone lines are susceptible to artillery fire, so repairing them would have been a vital and never-ending task.
As well as maintaining the actual comms network and equipment, he would have been responsible for ensuring all signallers followed SOPs wrt recording, logging and passing on all signals appropriately. He would also have worked with Brigade signallers stationed at Bn HQ to maintain good communications between 6th Bn and 2nd Bde HQ.
A few links of interest:
http://www.1914-1918.net/whatbatt.htmhttp://www.anzacsite.gov.au/1landing/s_signallers.htmlhttp://www.1914-1918.net/whatfieldcoy.htm