Besides the difference in missions and allowable questions (Stack Overflow helps you fix non-working code; Code Review helps you improve already working code), the two communities have different practices as well.
Stack Overflow prefers generic questions of general interest. Code Review prefers to see your code just as you wrote it, with all details that might be relevant to the review.
On Code Review, everything about the posted code is reviewable. Therefore, the code in the question must be preserved verbatim, including aspects that have no effect on functionality, such as whitespace, naming, and comments.
Code Reviewer answers may focus on a different issue than what the question asks. For example, the question might ask about how to write comments on a complex regular expression, but one of the answers might point out a performance problem instead.
On Code Review, there may be no single right answer. Answers may disagree. It's even acceptable for one user to post multiple answers (focusing on different aspects of the code or proposing different solutions to an issue).
Don't expect an instant answer. Code Review works at a slower pace, both because we are a smaller community and because it takes time to write a good code review.