Wakame is a dark green sea vegetable.
To reconstitute, soak it until soft, usually 15 minutes. Drain saving the soaking water for soup. Wakame will swell to about 5 times its dry size.
After soaking, cut out the central rib. Chop the rib very fine and cut the soft part of the leaf into bite sized pieces.
I like to use it as a garnish in soup, an ingredient in salad, or sprinkled over rice.