것, 걸, 것을, 것은, 건, 게
What are the differences and when would you use them?

것은
건
걸
것을
게

Is 건 just the contracted version of 것은? When do I use 건 and when do I use 것은?

Same question for 것을 and 걸

What about 게?

Question

것, 걸, 것을, 것은, 건, 게
What are the differences and when would you use them?

것은
건
걸
것을
게

Is 건 just the contracted version of 것은? When do I use 건 and when do I use 것은?

Same question for 것을 and 걸

What about 게?

Answer

건 is contracted version of 것은
걸 is contracted version of 것을
게,거 is contracted version of 것이

건,걸,게,거 are mostly used in conversation as a a colloquial expression.
것은,것을,것이 are used with formal, honorific language or in document, papers.

Answer

tricky question even for korean haha
Its not gonna be perfect but explain it at my best
것은 is simillar with greund when u wanna use verb as noun u can use this 
for example 먹는것은 즐겁다, 입는것은 어렵다
건 
걸
것을
게
and actually rest of them seldom use it i think it also is used for making gerund form
but the first one is most useful to remember because its the most frequently shown.
I think u dont need to worry about grammar too much if u keep speaking korean with korean friend u get proper usage of those things
I hope this answer would be helpful to u