Beans can be eaten at any stage of development.

Most people like to pick snap beans somewhere within shouting distance of pencil size -- though some individual varieties are bred for particularly skinny or particularly large beans.

If the bean seeds are distinctly obvious through the pod but are still soft they have probably passed beyond the snap stage into the "shell" or "shelly" stage where the seeds are stripped from the now leathery and un-palatable pods and used like fresh lima beans.

Once the beans and pods are fully matured -- the beans will be rock hard and completely dry while the pods are papery and brittle -- they are dry beans to be used in that form.