cooking with D.O without legs and round lid

With legs and a rimmed lid: campfire cooking. The rim on the lid holds the coals/charcoal in place and the legs allow coals to be placed underneath. This is the kind you will see at the Dutch Oven Gatherings.

Cast iron DOs with a flat bottom and domed lid are used on stove tops and kitchen ovens. The lids will have ridges or nibs on the underside to allow meats to self baste. The campfire DOs do not have self-basting lids.

Hope that's useful info for you.