Polarity is when a molecule has unequal distribution of charge (electron density). A molecule such as H2O would be polar, the charge is unequally distributed, Oxygen is more electronegative than H and therefore electron density is attracted to the oxygen more. This unequal distribution charge creates a + pole and a - pole on each water molecule. C5H12 doesn't have unequal distribution as does H2O and other polar molecules. This is pretty basic stuff though, I recommend reading any gen chem book.