Polar solvents have large dipole moments ( simply can be called charge difference); they contain bonds between atoms with very different electronegativities, such as oxygen and hydrogen.
Non polar solvents contain bonds between atoms with similar electronegativities, such as carbon and hydrogen (think hydrocarbons, such as gasoline). Bonds between atoms with similar electronegativities will lack charge difference; it’s this absence of charge which makes these molecules “non-polar”.