The most important things in Korean language is about speech level and honorofics. Please be careful about this things especially for the beginners.
Based on speech level, Generally Korean language is devided into two kind of level. Actually there are six level of the honorofics in Korean language. But I just want to discuss of two common level in Korean languages.
The first is 존댓말 jondaenmal a formal (polite) form.
Usually using with younger people to elder, junior to senior, or stranger people.
For beginners, this form is highly recommended for using.
The second is 반말 banmal an informal form.
Usually using with people who has higher status or older than a speaker. Such as parents to children, senior to junior, boss to the employees.
The word example of 존댓말 and 반말
English : "Hello"
존댓말 formal form : 안녕하세요 romanization : annyeonghaseyo.
반말 informal form : 안녕 romanization : annyeong.
English : "Thank you"
존댓말 formal form : 감사합니다 romanization : kamsahamnida.
반말 informal form :고마워 romanization : gomawo.
English : "Sorry"
존댓말 formal form : 미안합니다 romanization : mianhamnida.
반말 informal form : 미안 romanization : mian.
Although you are speaking with the same level of ages or status, please using the formal form.
Informal form is usually use for very very closed friends and is not recommended for foreigners or beginners.
(to be continued)