What is the meaning of each term in the grating equation, m(lambda)= d sin (theta)

If a grating has a ruling of 600 lines/mm, what is d, the spacing between the slits in nm (nanometers)?

Calculate all of the possible values of theta for light of wavelength 425 nm and of wavelength 670 nm using such a grating. (Remember that sin(theta) is less than or equal 1).