Dalton's law states that in a mixture of non-reactive gases, the total pressure exerted is equal to the sum of the partial pressures of the individual gases. It explains that each gas exerts a fraction of the total pressure independently and the molar fraction of a gas multiplied by the total pressure gives its partial pressure. Dalton's law allows us to determine the partial pressure of each gas in a mixture based on its molar fraction and the total pressure in the container.