By opening crates, each type of crate has it's own chance to drop a shard.
With these shards you can as an example craft crates or skins!
Example of shards:
Crates:
Bronze, Silver, Gold, Emerald, Legendary, Black Shard.
Bronze can only get bronze.
Silver can get bronze, silver.
Gold can get gold, silver and bronze.
Emerald can get emerald, gold, silver and bronze. Etc..
From Emerald crates or above also possible to get skin shards.
Skins:
Common Skin shard ~ Takes certain amount to craft a common skin!
Legendary Skin shard ~ Takes certain amount to craft a legendary skin!
Alternative for skins:
Split them by season shards.
(Spring, Summer, Autumn, Winter)
, but also great idea as always!