A polar solvent is composed of molecules, such as H2O, that have a discernible asymmetry in their surface electromagnetic charge. Water molecules consist of one oxygen atom single-bonded to two hydrogen atoms that are grouped together on one side of the molecule. This concentrates a negative charge at one pole.
Polar solvents dissolve similarly polar solutes. A good example of this is salt dissolving in water. Table salt is NaCl, or ionic sodium chloride. The extra electron adds a strong negative charge to the salt molecule and makes it strongly polar. Water readily dissolves polar solutes, while nonpolar solutes, such as oil, do not.