So you've had a great harvest of dry beans or peas, and your pods are fully mature and crispy. Depending on how many you have to deal with you could pop each pod open by hand, which is what we did for a number of years. It's especially nice as a group activity around a wood stove on Autumn evenings. If you have a lot of pods to thresh it's hard to beat a threshing box! I've been using my foot threshing box for years now, it's the most efficient technique I've come across for threshing larger amounts of beans, peas, lentils or grains. Table top hand threshing boxes are also an option.
I got the original design from Dan Jason of Salt Spring Seeds. It's super simple, just a 2 foot by 3 foot wooden box with a solid bottom and thin wooden strips attached to the bottom for extra abrasion. You pour the dry pods in (the drier the better), and do a threshing dance on them (music encouraged but not a requirement). Simply by crushing and rubbing the pods over the bottom slats you release the seeds, which are hard enough when dry not to be damaged by the process. Recently, I modified one side of the box to have extra thin slats, for more easily threshing smaller seeds like soybean and lentils (and even heads of barley and wheat).
Once all the pods are fully threshed, you'll end up with a seed and chaff mixture. It's easy to quickly separate the seeds by winnowing; pouring the seeds between two containers in the wind or in front of a fan. The light chaff blows away in the wind, while the heavy seeds fall into the container below. Usually in a half dozen passes the vast majority of the chaff will be gone, with just a few heavy bits and twigs to pick out by hand. We clean pretty much all of our seeds by winnowing… from large beans to tiny herbs. Light seeds like lettuce or kale just require more care so not to lose too many!