Shillings are the base currency in Lost Ark. You can basically use Shillings at Potion merchants to buy different potions. You can buy chaos Shards with them. You can repair your gear also costs Shillings. You can also do gear transfer enchantments with Shillings.
Your Epona daily tasks/quests will reward you with Shillings. You can complete 3 Epona daily tasks/quests to get a fair amount of Shillings every day.
The best dailies for the Shillings are in this area shown in the image. You can do these quests in the Headquarters Wind Roses. It is an island you can find the location given below.
In these three quests first, you have to go to the island and go to the terminal there. You can then accept these quests. These are really simple to do quests.
You now just have to go and talk to the NPCs in the harbor in each of the quest locations to deliver the parcel. You will complete the quest after talking to the NPC. You will then accept your rewards from them of the Shillings.
You can see the island is located in the East hangar near the Perian Sea.
You can use Epona weekly quests to get a decent amount of Shillings as well. These are the two quests recommended to do in Epona weekly that will reward you with over 100k Shillings that are decent for the grind you’ll have to do in these quests.
For the first quest, you can do the Chaos Dungeon that will reward you about 36k Shillings.
Next, you have to do Cube in your Epona Weekly that will reward you with 72k Shillings. You can get tickets for the cube varying level from doing the Chaos Dungeons.
You can also do Chaos Dungeon on your every character and get the rewards of your Shillings again. You can do Chaos Dungeons many times and it will reward you with decent Shillings every time.
You can use Silmael crystals and exchange them for Dungeon Explorer chests. There are variants for these chests and will reward you Shillings. For example, a small Dungeon Explorer chest will reward you with about 25k Shillings. You can also get the large silver chest that will give you about 10k Shillings in guild exchange for your Silmael crystals.