If not, you're missing out! They are delicious. Basically, a plantain is a green banana. It is lower in sugar than your typical yellow, sweet banana, and is more firm. Like the yellow banana, the plantain is a good source of potassium, as well as fiber.
Unlike the yellow sweet banana, which is eaten raw, plantains need to be cooked prior to eating. They can be used green, or allowed to ripen up more, turning a yellowish-black color. Either way, the plantain is delicious, and makes a great accompaniment to a main meat dish, especially pork :)
Here are some yellowish-black, more ripe plantains: they will be sweeter than the green plantain, as their starches have had time to convert to sugars, but still can not be consumed raw:
That's it - very easy.
So next time you're at the market, grab some plantains and try them out :)