Edamame are soybeans still in the shell. You boil them for a few minutes, drain, grind some salt on top to serve. You can serve them warm or chilled, although I tend to prefer chilled. Also, always serve with an extra bowl for the empty shells.
You can buy them frozen all year round, but right now, they are in season here in Okinawa (and will be gone soon, as the season here is always too short). So now is the time I can enjoy them fresh, and to take maximum advantage of this, I recommend a cold beer and enjoying them outside.