Your people need work and your town needs income. Trades turn residents into earners: bakeries and farms make food, blacksmiths and workshops make coin, and certain places generate afterglow - the light-stuff that powers your wards.
The names are plain on purpose. A tanner makes leather, a cooper makes barrels, a chandlery makes candles. Build a spread of them so a bad season in one trade does not starve the town.