Green mangoes are not a special variety of mangoes. They are simply unripe — not to be confused with Alphonso (a.k.a.) Indian mangoes.
On the dinner table, they are often chopped or grated, mixed with onions, tomatoes and bagoong (shrimp paste) to make a side dish with also doubles as a dipping sauce.
On the streets, the green mangoes are peeled, the stones removed and the fleshy portions are skewered. When you buy them, the vendor will provide you with the shrimp paste to smear all over the sour fruit.