Getting the seed out of the mango takes a bit of work. Once you remove the flesh the inner pit the next step is a bit delicate. Using a small knife scrap along the edge of the fruit, until you find the seem in the pit. Very careful crack open the pit, do not let the knife go very far into the pit. Once the pit has been cracked wide enough with the knife attempt to slide the seed out of the pit. There is a chance that the tap root may have formed careful separate the seed from the pit. The seed should look like a small clam.
It should look whitish with a brown skin layer on the seed. This skin will flake off when dry or can remain. My attempts have worked with both.
When going to plant the seed, place it on its side. Placing it just below the soil line as the start of the tree will start from the thickest part of the seed. As the tree starts to grow the seed will open up like a clam giving way to the tap root and tree.