Peel the mango skin off of the mango with a potato peeler or a knife. Be careful though, try not to peel off too much of the mango meat with the skin. Then grab a large bowl and shred the meat off of the mango with a grater.
The crushed pineapple can come from a can or you can make it homemade crushed. If you get it from a can, use a can opener or a knife to open the can. Then add the crushed pineapple into the same bowl as the shredded mango. Stir well together, then set aside.
You can get the shredded coconut from the nearest Asian Market or your local grocery store. I prefer going to the Asian Market because they have a good quality and very cheap :). The shredded coconut is usually frozen so I recommend putting the frozen bags in a pot that is full of water so it can melt. Once melted, cut open the bag and pour the coconut into the same bowl as the pineapple and mango mixture.
Open the can of coconut milk and slowly pour in little by little into the big bowl that has the mixture of fruits in it. Mix well and pour in most of the coconut milk or until the amount has come to your liking. Pour in the water as well and make sure you don't pour in too much liquids because the Otai is not supposed to be very liquidity. It is supposed to be not very thick as well but it is thick and yet liquidity.