When do Koreans use exclamation mark '!'
I know that ~ makes the sentences much more friendly and longer but when do Koreans use '!'
When they use it, does it mean they are angry? Cause '!' Is usually used for command

그래 sounds ok and normal but if a person says 그래!!!! After I says 난 이제 공부할거야, does it mean that person is showing frustration?

Question

When do Koreans use exclamation mark '!'
I know that ~ makes the sentences much more friendly and longer but when do Koreans use '!'
When they use it, does it mean they are angry? Cause '!' Is usually used for command

그래 sounds ok and normal but if a person says 그래!!!! After I says 난 이제 공부할거야, does it mean that person is showing frustration?

Answer

I believe the exclamation mark is not used in any different way in Korean than in other languages like English.
It expresses an emphasis, a surprise or other deeply felt emotions, which could include anger but it would be rare.

Also note that a lot of punctuation marks used on the Internet is nonstandard and not used in a serious writing.
For example, "~" is rarely used and repetitions like "!!" is not used in professional writing.

If someones says "그래! 난 이제 공부할 거야.", it is most likely expressing a resolve.
The person is saying "Yes! I will study from now on.", and "!" probably shows a strong determination in his/her heart.