Dandelion Greens are a member of the sunflower family, the green leaves are picked before yellow dandelion flowers develop. These greens have slightly bitter taste, similar to chicory and are most frequently eaten raw in salads but they may also be cooked, prepared as you would spinach. Even the roots can be roasted and ground and used to make a "root coffee" like chicory coffee.
You can purchase these greens in many well-stocked grocery stores including Whole Foods Markets or at farmer's markets and even Asian markets.