It's a kind of seaweed, loaded with minerals. Nice on top of fish or veggies,
If it's dried. Soak it and use it in miso soup.
It's also good with salad with a sesame ginger dressing, or noodle bowls.
It's a bit more 'thin' than wakame (which is used in salads, soups also) which makes it a nice garnish (as Wssmom mentions.
I love it in a vinegary salad with rice wine vinegar, icewater, a touch of sugar and soy sauce; cucumber (sometimes diced tomatoes and seafood, like crab, or shrimp).
If you find it fresh...you're lucky. Garnish bits or vinegar based salads.