When we use English, we cannot use two verb in a clause. So we have to make a verb to 'to-v' or '-ing'.
Like English, we can change the form of verb in Korean.
For example, in this sentence 나는/ 영어 공부하기를(to study English) /원해. (I / want / to study English.), we have to make a verb 공부하다 to 공부하기.
Actually, it's so difficult to explain, even though I'm a Korean. :)
If you have more questions, please let me know.
Have a nice day~