It's too convenient, because I went on a weekend and it's usually very crowded, so I booked a ticket on traveloka. The ticket exchange process is extremely convenient. After ordering, it takes about 5-10 minutes (maybe 24 hours if the system is crowded). An email will be sent with the KR Pass card. When you have a KR Pass card, go to the korail website to book a seat and choose a time. Please note that when the booking is successful, there will be a QR code, so you should print it out or save that page as a pdf to print later. Once printed, you will go to Seoul Station (or Busan Station), look at the information board and look up the correct train number (on the ticket) to find the track number. You will wait for the train right on the right track, when the train arrives, find the correct car. and chairs.