Hi Vinit!
Salts melts the ice and helps to keep water from re-freezing. This is done by lowering the freexing point of water. And this phenomenon is called freezing point depression.

It is only achieveable when there is some amout of liquid present. The more particles (ions) formed when a salt dissolves, the more it lowers freezing point.

When salt is added to ice, it first dissloves in the film of liquid which is present on the surface, and hence reducing the freezing point below the ices temperature.  And now ice is in contact with the salty water, so it melts by producing more water and this cycle goes on until the ice completely melts.

Thankyou!