-는 것 (-는 거) turns a verb into what is called a "gerund" and allows it to function like a noun. "Running," "swimming," and "eating" are a few examples of gerunds in English. -는 + verb means the act of, and 것 means "thing," so you could literally translate it as "the ~ing thing". 것 is sometimes written as 건 rather than 것은 when it is the topic, 게 rather than 것이 when it is a subject, or 걸 rather than 것을 when it is the object. 수영하러 가는 게 좋아요. - I like going out for a swim. (가는 게 - the act of "going") 다 가지고 오는 걸 깜박했어요. - I forgot to bring all of it. (literally "I forgot the act of bringing it all) "~걸" comes from 것 + the object marker 을. It just turns whatever "thing" you are referencing into an object. If the entire sentence ends in "~걸" it takes on the extra meaning of either being contrary to what you might expect, or that you are stating matter-of-factly. 원하는 걸 살 수 있네요! - I can finally buy that thing I want! (원하는 걸 - that thing I want [as an object]) 어제 잃어버린 걸 아직 안 찾았어요. - I still haven't found that thing I lost yesterday. (엃어버린 걸 - that thing I lost [as an object]) 그걸 깨버렸어요 - I accidentally broke it (that thing) ~으며 means "while," "during," or in some cases "and." You would use it when you mention that one action is happening at the same time as another. verb + ~(으)며 + the rest of the sentence. 그사람 울으며 얘기하려고 했어요 - She was trying to talk between sobs (lit. she was trying to talk while crying) 커피를 미시며 우린 서로 좀 알게 됐어요. - We got to know each other a bit over coffee.