Sorter mean the one who sort the past cards depends on the pin code. They separate the postal cards, letters and speed posts depending on the To address and distribute according to pin code.
Group D is the division in the post office and it is the lower category posts like Peon, Orderly Peon, Choukidar, Choukidar-cum-Sweeper, Gardener, Collection Peon, Night Watchman, Sweeper, Process Server, Treasury Peon, etc.
The Postal Department of India recruits staff for Sorter and Group D posts depending on their eligibility and skills. Now days to become Group D officer they need to know the DATA ENTRY OPERATION also.