Make sure you purchase Lost Ark Gold the Founder's Pack.
Log in to the game and click on the icon for the box that shows an arrowpointing towards it.
This icon appears on the top left corner of your screen.
When you click on the box in the middle, you'll view what you have in your Founder's Pack, press on Claim.
Start your Inventory.
Click right-click to open the Founder's Pack.