Normally, there are 3 ways to apply for a S. Korean visa: e-visa, Korean diplomatic missions abroad, and Korean immigration offices. Unfortunately, E-visa issuance has been suspended because of Covid 19.
According to Korea Visa Portal, you should submit 5 documents when you apply for a visa: the visa application form, scanned passport image files, a digital photograph, and the fee and other specific required documents for respective type of stay. If you want to download the application form, please visit https://www.hikorea.go.kr/board/BoardApplicationListR.pt
Depending on your country's rules, additional documents or processes may be needed.
After accomplishing these requirements, just wait for their review. If all goes well, you should be able to get your visa shortly.