It's a fun word with multiple meanings.
First, it means 'completed'. For example, if you say '시간이 됐네요', it means that you are approaching the time you have decided to do something. Or '밥이 됐네요' means that the meal is ready for you to eat. In this case, it has a positive meaning.
In the following meaning, it means 'that is enough'. In this case, it has a strong negative connotation. For example, if someone asks 'Shall we eat together?' and you say '됐네요', it means that you do not want to eat with that person.