You add it to a verb stem to indicate a question. Generally, you don't use it with adjectives. For that, use -ㄴ가요/-는가요 instead.

It's used in place of -아/어요. It sounds a bit feminine and informal, but many men use it as well. 거기 비 와요? 거기 비 오나요? 지금 오고 있어요? 지금 오고 있나요? 누가 전화했어요? 누가 전화했나요?