The basic idea of Community Supported Agriculture is that a member pays a set amount upfront in the winter (when farmers need cash to get the operation up and running) and then thoughout the growing season, they get a mix of what is available each week in return. This helps the grower when they don't have any profits coming in, and in turn makes eating fresh, local food that much more affordable.
All farms operate their CSA's a little differently, following is the basics on how ours works. We charge per share to be a member of our CSA. There should be 16 weeks of our growing season, when we are able to offer farm grown items for sale. On a tuesday, wednesday or thursday, you come to the SIW farm stand and pick out and weigh your own stuff. We have a list on our CSA Board that lets you know what items are part of the share for the week. You also get a discount on other stuff and get free compost.