While this site is in private beta, every user can vote to close a question. Closing a question takes 5 votes. Every user can also vote to reopen, which again takes 5 votes.
The private beta is the phase where the site starts to take shape. It's especially important to decide now what is suitable for the site and what isn't.
If you see a question that is not suitable for the site, vote to close it. We're getting quite a few questions that do not have precise enough requirements. During the private beta, we define the expected quality. If a question is not good enough, it's vital to say so. So vote to close, and leave a comment explaining why the question is unsuitable and what can be done to improve it.
If you come back later and the question has been improved, rescind your close vote if the question is not closed yet, or vote to reopen otherwise.
If a discussion starts in comments, ask a meta question to bring the attention of the community to the issue, which may be applicable more generally than the question that sparked it. Be sure to link the main site question in your meta question, and to leave a comment linking to the meta question under the question on the main site.
The same goes for answers. If you see a bad answer, downvote it and leave a comment. If you think that certain answers do not meet some minimal quality requirements, at this stage, it would be best to discuss those requirements on meta. If you see a good answer, of course, upvote it.