Brown lentils are the common "grocery store" variety found throughout the U.S. Lentils can be cooked in water with a few seasonings or combined with broth, ham, or ham hocks and other vegetables. They are best not overcooked because they'll become too soft and mushy.
As with other dried beans or legumes make sure to pick over lentils carefully before you cook to locate and remove any small pebbles. Organic lentils have become easier to find and priced competitively so look for organic where available.