You cut the green skin off, slice it in half, scoop the seeds out, then slice it in thin (1/4") crescent shaped slices. You soak it in salt water for a while, drain and dry off slices and then fry in coconut oil. It has the flavor of potato, but is much more creamy in texture.
I don't think there is a "ripeness" test, only size. If its a certain size its o.k. to harvest form the tree.