One of the ways to use 还是 (háishì) is to have it mean "you had better," similar to how in English we may say "I think you had better start on your homework." in Chinese grammar.
还是 as an adverb can express "had better" or "it would be better to". The idea is that the speaker has given the matter some thought, and after considering it, has finally come to a decision. The announcement of this decision will frequently include 还是, and it usually comes before a verb or a subject.
吧 is often placed after this structure, as it’s a suggestion.
你 不 会， 还是 我 做 吧。