How to read the Lost Letter in Crimson Desert

So you've been wandering around in Crimson Desert and met a very suspicious stranger, who handed you the Lost Letter before disappearing into thin air. Well, now what? That's a good question, and you're not given any hints as to what the stranger wants or how to even read the Lost Letter.

Your natural reaction was probably to check your inventory, only to come up short-handed. That's not a problem with you; it's Crimson Desert's confusing UI. So, here's what you need to do with the Lost Letter.