In Korean there are different formality levels. Depending on the situation and the person you are speaking to, you’ll have to decide between formal, polite/casual, or Informal speech.
That being said, even the word “I” and “You” have a formal and not so formal form that you have to be aware of.
저 = I (used in formal speech, also usually used in polite/casual speech)
나 = I (used in informal speech)
As for the polite/casual form, you may see some people pair 나 with 요 (polite/casual sentence ending). While some say that it is incorrect, many Koreans do use it this way.
But when you switch the pronoun, you must also switch your sentence endings to match.
저는 한국어를 배워요. → I’m learning Korean. (Informal)
나는 한국어를 배워. → I’m learning Korean. (Informal)
Like I mentioned above you may see some Koreans say sentences like:
나는 한국어를 배워요. → I’m learning Korean.
WHAT ABOUT “YOU”?
당신 = You (used in formal speech)
너 = You (used with informal speech)
The argument can be made that Koreans don’t actually use 당신 all that often as it can seem rude, but technically it is the word for “You” and it is formal. Instead of this, Koreans will often use titles and names instead of just saying “You”.
View related lesson:
Click to read - 저는 vs 전 | 나는 vs 난 | 넌 널 날