A solution is formed when a solute is dissolved into a solvent. An example is the sweet solution that is formed when sugar is mixed with water or the salty solution that is formed when common salt is dissolved into water.
In comparison, when sand is added to water, it does not mix, and no solution is formed. Because the sand is heavier than the water, it will ultimately settle down at the bottom of the container. The resulting product is, in fact, a mixture.
The mixture of sand and water can be separated out by physical actions of filtration and drying. Water containing sand can be filtered to separate out sand and then dried to obtain dry sand (the original material we started off with).
Hope this helps.