K-ETA is an electronic travel authorization form that foreign visitors need to obtain before entering Korea visa-free.
If you are planning to apply for K-ETA, you must complete the application form within 72 hours before your flight. K-ETA is valid for 2 years from the approval date.
The K-ETA application process is not complicated: agree to terms and conditions, then enter your email, passport information, and other details. After paying the 10,000 KRW fee, just wait for the assessment and results.
See more details here: https://www.k-eta.go.kr/portal/apply/index.do
ROK missions overseas also provide K-ETA instructions by country.
View them here: https://www.mofa.go.kr/eng/index.do
Image Source: Ministry of Justice