1) ㅋㅋㅋ came from the word 크크크 (kekeke) which is the sound of laughter
2) ㅎㅎㅎ came from the word 하하하(hahaha) which is also the sound of laughter. You can also use 히히히(hehehe) 호호호(hohoho)
3) ㅠㅠ or ㅜㅜ resembles the crying emoticon
4) 애교 Aegyo : To be cute generally or act cute
You can watch this video
for more detailed explanation ^^
5) 대박 Daebak : Literally means big win, Hanja (大发) but this term is commonly means Awesome!
6) 파이팅 (Konglish: Fighting) / 화이팅 [홧팅-Some native korean would type this shortcut] : Cheer someone as a form of encouragement. Similar meaning with 加油 or all the best~
7) Adding ㅇ to the 받침 Final consonant of the word. Generally the younger generation will use this to make it sound more friendly, informal and cute.
Eg. 오빠! → 오빵!
[용] Substitutes for ~요 at the end of sentences