Everyone’s given good airport advice, so I’ll offer some personal travel advice if you’re not a frequent traveler.

Keep your personal travel documents in a place you’ll remember in a bag close to you, under the seat in front of you. Same for any medications. Purse, tote, backpack, whatever, and make sure it’s in a place where it’s zipped up and won’t fall out of the bag when set down. This means your passport and any other ID, and even your bank cards and the like. This bag will not and can not be checked luggage. Make sure it conforms to carry on bag restrictions for the airline.

Do not carry important items in a disorganized jumble at the bottom of a bag. You don’t need that panic desperately digging for a passport, checking pockets, jackets, whatever, while freaking out that the item may be lost. Keep organized. You’re going long way and are going to be wiped out physically and mentally. Save yourself the stress.

Do NOT put anything in the seat back pocket. After hours and hours of stress of travel and fatigue you will be far, far more likely to forget you put something there. Phone, backup battery, itinerary, or heaven forbid a passport. I travel for a living and probably just over once every couple months the cabin crew find a passport or phone in a seat back or a passenger comes running back to the plane panicked looking for an important item.

Customs - make sure you don’t bring anything you’re not supposed to into another country. Some innocuous over the counter medications like decongestants based on stimulants are illegal and treated like illegal drugs to bring in to some countries. Check Korea’s laws for travelers before you depart.

Give yourself time to get through airports that are unfamiliar. This includes time to clear customs and security. This will also help reduce stress and give you time to recover from any missteps like showing up at the wrong terminal.

Good luck, enjoy the ride!