A + in the box indicates that you are long-sighted which means you find it difficult to see things close to you. A – shows that you find it hard to see things that are far away without glasses.
The amount of astigmatism (visual distortion) that is caused by an irregularly shaped cornea. An empty box means there is no astigmatism and your eyes are perfectly spherical. A low number like 0.25 means your eyes are not quite round and a higher number like 3.00 means your eyes are quite oval.
The direction of the astigmatism, measured in degrees. This is more for the lab to know how to position your lenses.
This usually indicates that your eyes do not work well as a pair. Prism lenses will provide the correction you need and help prevent double vision or headaches.
The base simply tells the lab where to put the prism in your glasses.
ADD - If you are over 45, you may have a number here. This is your reading addition and relates to the amount of additional correction needed to focus at close distances. A measurement will mean you have different prescriptions for distance and reading.