After every eye exam we hand over a slip with a small table on it. Most people fold it into a wallet and never look at it again. It is worth a minute.
SPH, the sphere, is the main strength. A minus number means short sight: things far away are blurred. A plus number means long sight. The bigger the number, the stronger the lens.
CYL and AXIS come as a pair. They describe astigmatism, an eye that focuses more in one direction than another. The cylinder is how much, the axis is the angle.
ADD appears from about forty-five. It is the extra help for reading, and it is what turns a single vision lens into a varifocal.
PD, the distance between your pupils, decides where the optical centre of each lens sits. Online shops often guess it. We measure it.