There are many answers that don't really answer the question being asked, such as the following one, but you can easily find other when you look at the first posts in the review page, or in the low quality posts list.
@pushka I am having the same problem. Did you find an answer?
That has been posted as answer, but it doesn't answer the question at all; it is asking a question about the question, and it should be better written as comment.
When you see such answer, you should flag them as "not an answer." Similar answers that should be flagged are the following ones:
Thank you guys, this helped me!
I don't understand your answer; can you explain me more?
Give us more details, and you will get the right answer.
I am not sure I understand your question.
The flag "not an answer" should not be used for wrong answers, though. It should be used for something that is not an answer at all, such as asking for more details, or asking to the OP if he got an answer, or asking a completely different question.
To make it more clear, suppose that somebody asks "What time is it now in Italy?" (right now it is 3:27 PM), and the question gets two answers:
It's 6 AM.
I am interested in knowing what time is in India. Can anybody help me?
The first answer is a wrong answer since the correct one should have been 3:27 PM; the second answer is not an answer at all, as it is asking a new question that should not be posted as answer.
As for answers that merely contains a link, while those can answer the question, they are not the preferred way of answer a question on Stack Exchange. If you find any of them, leave a comment similar to the following one.
While this link may answer the question, it is better to include the essential parts of the answer here and provide the link for reference. Link-only answers can become invalid if the linked page changes.
If then the user doesn't expand the answer to add more details, then you can flag it for moderation attention, using "not an answer" as flagging reason. It would be better to wait at least 5 days before flagging the answer.
TL;DR Everybody can flag posts, as it requires a reputation of at least 15; find an answer that is really a comment, a new question, or gibberish, and flag it from the question page. There are many posts that should be flagged. Let's make Drupal Answers a better place!
If you have the necessary reputation you can review the first answers (if your reputation is at least 500), the late answers (500), or the low quality posts queue (2K) to find answers that should be flagged. The "first answers" queue shows the first answers given by new users, who post as answer something that should be a comment, simply for the fact they don't have the reputation necessary to comment on questions asked by other users, if they didn't get the association bonus using the same OpenID account on more than one Stack Exchange site; the "last answer" queue shows the new answers given for old question, which could include also those "Did you find a solution?" answers given from low reputation users who created the account months ago, and then didn't participate much to the site; the "low quality posts" queue allows to find out posts such as "me too!" but also spam.