There are many places where you can buy transportation cards in Korea. Here are some of the most common places:

• Convenience stores: Convenience stores such as CU, GS25, and 7-Eleven are the most common places to buy transportation cards in Korea. They are usually located near subway stations and bus stops, so they are very convenient.
• Subway stations: Most subway stations have vending machines where you can buy transportation cards. These machines are usually located near the ticket gates.
• Tourist information centers: Tourist information centers in major cities also sell transportation cards. These centers are a good option if you are not sure where else to buy a card.
• Airports: You can also buy transportation cards at the airports in Korea. This is a good option if you are arriving in Korea and need a card to get around.

The most popular transportation card in Korea is the T-Money Card. It can be used on buses, subways, and some taxis in most major cities. You can also use it to make purchases at some convenience stores and shops.

Here are some of the other popular transportation cards in Korea:

• Cashbee Card: The Cashbee Card is similar to the T-Money Card and can be used on the same transportation systems.
• MuniPass Card: The MuniPass Card is a rechargeable card that can be used on buses and subways in Seoul.
• Seoul City Pass: The Seoul City Pass is a prepaid card that includes unlimited rides on buses and subways, as well as discounts on attractions and tours.

When you buy a transportation card, you will need to pay a deposit of 500 won. This deposit is refundable when you return the card. You can also buy a card with a design, but these cards will cost more.

To use a transportation card, simply tap it on the reader when you enter and exit the bus or subway. You can also use it to make purchases at some convenience stores and shops.