This is 800g of mango seeds. As a guideline, this usually means about 56 seeds. Mature mango trees regularly bear 200 fruits per year, or 30-40kg.
The seeds should be scarified before planting. Then plant them in nursery trays with goods drainage in a semi-shaded place, leaving 15-20cm between seeds. Mango thrives in warm climates. When the seedlings are big enough, move them to a well-drained sunny spot.