thank you Mojave for your comment, I think it's used more used in spoken and slang than It is a grammatical structure ; and I need more time to be able to understand it _ I did find an explication here, but I can't understand what it is written - http://bbs.enjoykorea.net/thread-202604-1-1.html hope someone can translate it into English

-는 can be used to turn a verb into a noun modifier. 걸 is the short form of 것을 which is the noun 것 + the object particle -을. Together they make a "noun group" - that is a noun form of a verb.

thanks youni for your comment , I checked naver and daum but It is too hard for me to understand what is written in korean, thanks again

Have you ever tried using Naver dictionary to look up the meaning?