To order the correct glasses you need, the very first step is to know what your new glasses are used for. Sometimes your eye care provider writes it down on your prescription. 'DISTANCE' and 'READING' are all single vision glasses but designed for different people.

DISTANCE is for nearsightedness (have trouble seeing far away) and farsightedness (have trouble seeing up close). If you are nearsighted or farsighted, choose DISTANCE as your glasses usage and enter what your prescription says.

However, the READING section is designed for people who have presbyopia that is an age-related condition. It generally starts to appear around age 40. People who have presbyopia cannot read or use a tablet computer without reading glasses. So if you have this eyesight issue, choose READING as your glasses usage.
READERS are used for seeing up close between 11 and 16 inches (27-40 cm), like reading books.
INTERMEDIATE is for seeing something at 20 inches (50 cm), like using a laptop.