Polar substances tend to dissolve well in other polar substances, but not nonpolar substances, while nonpolar substances dissolve well in nonpolar substances, but not polar substances. This concept is often referred to as "like dissolves like."
An example of a good polar solvent is water. Water is known as the universal solvent due to how many polar substances it can dissolve, which is a result of the strong attraction that the hydrogen and oxygen atoms can exert on other substances. Salts and sugars are two examples of substances that readily dissolve in water. An example of a good nonpolar solvent is hexane, which can dissolve most nonpolar substances.