considering the question is talking about dry sodium chloride we can assume that it is dissolved in water and was formed by a reaction such as NaOH(aq)+HCl(aq)⇒H₂O(l)+NaCl(aq). since the sodium chloride is dissolved in water, you have to some how get rid of the water. This can be done by heating the sample or letting it sit for a while since both of those actions would cause the water to evaporate. as the water evaporated, you would see white crystals starting to come out of the solution (precipitating out). Once all of the water is gone, you would be left with the white crystals which would be pure sodium chloride.
If I had to do this in a chemistry lab, the procedure would look something like this.
1. obtain or make a sodium chloride solution.
2. heat the solution over a Bunsen burner until all of the water boils away so that you are only left with sodium chloride crystals.
I hope this helps. Please let me know if anything was unclear in the comments so that I can explain further.