Use Learn Korean Language (see Resources below) to learn Hangul, the writing system of the Korean language, which is made up of 24 letters. Though you may plan to do any writing in Korean if your aim is only to learn greetings, knowing the simple writing system will help you use all other resources you use while learning elements of the language.
Use a Korean phrasebook or travel book to learn Korean greetings. Lonely Planet's Korean phrasebook offers an entire chapter on greetings, including farewells. Lonely Planet uses an easy-to-read transcription method to help you pronounce greetings and other phrases correctly.
Visit Planet ESL (see Resources below) to learn about the appropriate bowing and handshaking rituals that are paired with Korean greetings. The basic Korean ritual when meeting someone is to shake with both hands while bowing and saying your greeting.
Practice your greetings. Ask a Korean-speaking friend or another student of Korean to work with you on the greeting ritual, and, when you feel comfortable, try your hand at greeting Korean-speaking people you meet in their own tongue.