It is the same as you read prescription for regular glasses. And there is no difference between rx for reading glasses and regular glasses. On your prescription, you can see characters SPH, CYL, AXIS, and ADD. And the different character stands for different vision problems and their strength are used to make different eyeglasses.
SPH= Sphere=Spherical, is the strength of your prescription, bears sign "+" or "-", "+" use for make regular single vision glasses.
CYL= Cylinder= Cylindrical, is the diopters degree of the astigmatism. And AXIS, is a number between 0 and 180 degrees, and means the orientation of your astigmatism.
ADD= Near Addition, means the power strength to be added to the Sphere number for making single vision reading glasses.