Hi, I just answered your popcorn question and the answer is the same for sweet corn. I'll re-post it here though.
Not unless you grow a ton of corn, you can not save seed. Corn is one of those plants that must be grown in large quantities, at least 200 plants, for seed saving. It suffers from inbreeding depression. Plus, it is wind pollinated so if you live anywhere near where corn is growing it will cross unless proper bagging procedures are followed. So it is unfortunately one of the few vegetables that seed is best purchased.

Beans on the other hand are quite easy! You just need to let pods mature on the plant. The bean seeds will swell in the pods. Do not remove them until the pods are dry. You can tell they are drying. They have color changes as they dry. Once they are dry, when you push on the pods, they will split at the seam easily. Gather them up at this point. Take them inside and shell them all. Leave out on plate to dry more. Though they seem dry, there is small amounts of residual moisture that must still come out of the beans. Leave them sit on the plate for a few weeks. Check to make sure they are completely dry by taking a hammer and smashing one on your driveway or other hard spot outside. If it smushes, it is not dry enough. If it cracks apart, then it is dry. (Or let them stay out on the plate for over a month. They will be dry enough by then.) When dry, put the beans in your freezer for a couple days to kill any weevils that might possibly be in some beans. You do not want your beans to be ruined in storage by weevils. When you take the beans out of the freezer, let the container you put them in come to room temperature before removing the beans. If you do, you'll kill the beans. Once at room temperature, put in a paper envelope, label, and store in a cool, dark, dry location.
Remy

Remy - thanks for the info on both threads. The beans seem easy enough.