어때요? is like "how about VERB-ing?" or "What do you say to VERB-ing?". As with those English phrases, it requires a noun form or conditional clause after it, and -는 게 makes that noun phrase. It is a contraction of -는 것이, where -는 것 (doing something) is a gerund equivalent and 이 marks it as the subject. For example, 사는 것 (living), 공부하는 것 (studying), 이기는 것 (winning) are all noun phrases that can be used anywhere a noun is suitable. -는 게 어때요? is a common way to ask what someone thinks about a suggested activity. Another way to say it is with the -(으)면 form of a verb which creates a conditional clause: - 한스 씨, 같이 좀 걸으면 어때요? = Hans, how about if we walk together for a while?

I dont know i just start learning korean