You don't.
You catch Pokémon underwater which hold shards, then you trade those shards with the treasure hunter for evolution stones.
The green shard can be traded for a leaf stone if you talk to the Treasure Hunter on Route 124. Any shards can be traded in for an evolution stone. Yellow Shards = Thunderstones Blue Shards = Water Stones Red Shards = Fire Stones Green Shards = Leaf Stones However there are no shards that allow you to receive a Moon Stone.
You can trade them for evolution stones eg. yellow shard = thunderstone
there is this guy in the sea at sunyshore city then you talk to him and he changes all the shards into stones or you can buy the NDS action replay ultimate code for Pokemon and get 999x stones of every kind
There is a person on an island just above Mossdeep who will trade colored shards for evolution stones. (red-firestone, yellow-thunderstone, ect)
Yellow Shards and the other color shards are used for trading with NPCs for items or moves. For example in Pokemon Ruby, Sapphire and Emerald they are the main source of evolution stones.
find the guy who collects shards and trade shards for stones
you can trade shards for stones in hunters house. His house is southwest of mossdeep.
you get stones for shards from some persons house west of mossdeep
They can be traded for evolutionary stones.
With the shards you collected, you can travel across the sea and find a house in the midst of the ocean. This house can be found near the Mossdeep city. You can trade these shards into useful evolution stones. The color of the shard corresponds to the color of the stone that he will give you. Red Shards â–º Fire Stone Blue Shards â–º Water Stone Yellow Shards â–º Yellow Stone Green Shards â–º Leaf Stone
All stones must be obtained by trading shards to the hunter west of mossdeep city shards can be found underwater near the hunter's house.