It can be used by sending out a compatible Pokémon and right-clicking the Pokémon with the Leaf Stone. The Pokémon will evolve into the corresponding evolution.
A Leaf Stone is crafted with nine Leaf Stone shards. Leaf Stone shards can be found within the leaves of trees. They resemble leaf blocks with bright yellow patches on them. Each Leaf Stone ore will drop one shard, so it is necessary to find nine ore.