how do i buy stuff with blue essence and orange essence???

blue essence you can get by buying champion tolkens in the shop, rolling it, and dismantling the shard. orange is when you get skins from chests

The essence is used for upgrading shards you get from the loot system into permanent items, orange for cosmetics and blue for champions and champion mastery (You need a shard from the loot system in order to use the essence for upgrading). You can obtain either essence by instead breaking down an unwanted shard, and for blue essence you are able to buy a "Hextech Mystery Champion Shard" from the shop under the accessories tab in order to get a random champion shard to break down into essence.

Did you figure this out? The only things I see in the store can be purchased with RP (and some with IP) but none with Orange or Blue Essence.