Why does table salt help melt ice on sidewalks?

Answer: Dissolved salt lowers the freezing point of water

Dissolving salt releases enough heat to melt the ice — Dissolving ordinary table salt absorbs a little heat rather than supplying the heat that melts ice. Its useful effect is to lower the freezing point of the water on the ice. Other deicing salts can release heat, so the kind of salt matters.

Salt makes ice too slippery to remain solid — Making a surface slippery does not turn solid ice into liquid water. Salt works after dissolving in a thin layer of water, allowing liquid brine to remain at temperatures where pure water would freeze.

Dissolved salt lowers the freezing point of water ✓ — Dissolved salt lets water stay liquid below the freezing point of pure water. Salt on ice forms brine in the surface water, so more ice can melt if the surroundings supply heat. The freezing point depends on salt concentration; salt becomes less effective in very cold conditions.