-는 is a verb ending that describes a noun. -는 것 is a noun phrase that can function like a noun. The -는 것 phrase usually means the act of doing something, like a gerund in English, but it can also mean an object or target of the action if the verb has such a meaning. For example, 먹는 것 has two meanings: 1) to eat or eating, 2) things to eat, i.e. food. In the majority of cases, -는 것 describes the action itself: 사는 것(to live, living), 남을 이해하는 것 (understanding others), etc. E.g. 때로는 지는 것이 이기는 것이다 = Sometimes, to lose is to win. 것 is just one noun (although it is a rather widely used one) that can be used with -는. It is used when the action is in the present tense, either describing what's happening now or denoting something that generally happens. There are other forms like -(으)ㄴ, (으)ㄹ, and others if the action is in the past or future tense. - 공놀이를 하는 아이들 = kids playing with a ball. - 주말에도 열심히 일하는 사람들 = people who work hard even during the weekend. - 내가 마시고 있는 (이) 드링크는 맛있다 = The drink that I am drinking is delicious.