A non-polar solvent is one with molecules that have roughly the same electrical charge on all sides; in other words, it has low static permittivity. Non-polar solvents are typically hydrocarbons, such as pentane and hexane.
Each atom on the periodic table has an electronegativity value that describes its ability to bond to other atoms. If the difference between two elements are small then they have a non-polar bond. For an entire compound to be non-polar, all of the electronegativities of the atoms in the compound must be similar. Non-polar solvents also have no partial charges due to their small differences in electronegativities. These solvents dissolve all types of non-polar compounds.
Non-polar solvents are used to dissolve other hydrocarbons, such as oils, grease and waxes. Hexane, for example, is used to extract canola oil from seeds. While it is dangerous, gasoline is still a commonly used non-polar solvent to remove contaminants from metal parts. However, non-polar solvents are generally ineffective against sugars, salts and other charged molecules for which a polar solvent, such as water, is appropriate. Non-polar solvents and polar solvents do not dissolve within each other; mixing water and gasoline, for example, leads to the gasoline floating on top of the water. While the gasoline and water do attract each other slightly, the water's polar molecules are much more strongly attracted to each other.
Soaps contain both a non-polar component and a polar component. In a soap, the non-polar tail is attracted to non-polar grease, while the polar head is attracted to water. This lets the soap dissolve non-polar contaminants in water; adding soap to a mixture of water and gasoline allows for the two to be combined in an emulsion.