Question

why sodium chloride is added to water with constant stiring

Answer 1

This is because stirring allows more water to come in contact with sodium chloride,thus making the sodium chloride dissolve faster.Also if you just put sodium chloride in water without stirring ,it will settle down at the bottom and start dissolving.When it dissolves like this ,the water near it will be more saturated than the water away from it i.e,at the top.The dissolution process is very much slower in saturated solution .You can also heat the water to make the sodium chloride dissolve faster.