Mangos are tricky to cut. Without this gadget, there is more waste than is necessary. The pit is an odd shape and you have to know how it lays inside the fruit to know how to cut the fruit. Using this handy gadget eliminates the mystery.
Set the Mango on one of the its ends. Push down. You will be left with 2 halves and what appears to be solid fruit but is actually the pit. Discard the pit.
Using a sharp knife, score each half, making cuts spaced 1/2" apart, first in the lengthwise direction, then perpendicular to those cuts. The skin has a concave shape. Place your fingers on the outside of the skin and push upward to make a convex shape. Run the knife along the inside of the skin releasing the cubes of fruit. Hopefully these pictures will help you.