First, you buy a ready mango, a local one or an imported one that wasn't treated, in order to have a good seed. I advice you to have an ataulfo mango that comes from Mexico, they are not treated and ataulfo mango they call it champaign mango or honey, it is a cousin of alphonso mango, so sweet, no leaves and a wonderful aroma. It is a cousin of alphonso but with a different shape and most of all you can find it in the Lebanese market.
Second clean the seed from the outside and let it dry for one or two days. After take the outside shell carefully, not to damage the inside seed. Wash it with a clear water, and try easily to take out the brown coat that envelopes the seed. After you take a sort of plastic with a cover, similar to the one you get when you buy a mini tomato, you put inside a wet cotton, you put the seed inside and cover it all with the wet cotton. Put it in a warm . Check from time to time to see if the cotton is wet. After a few days or a week it starts to germinate. When you see that the seed germinating, bring a pot, put at the bottom some stones for water evacuation. Prepare a mixture of sand without salt, river sand with soil from the garden and with tourb (compost) mix together, give water and put the seed. Usually the seed looks like an arc, put the arc down, you can't miss because you will see the roots, and the back up. Cover with approximately 1 cm. And 'keep wet,in a warm and if possible sunny place. After a week or more depends of the season you put in, you can see the mango plant growing. When the plant is about 40 cm, you can plant it in the garden.