OK, I asked a question, and it gets answered. I don't want to bother anyone anymore, so I want to mark my question as answered and consequently closed. How do I do that?
If you get answer from any of the proposed answer, you can check the grey tick mark on the left side of the answer. In this way, It will be marked as having an accepted answer.
If you don't get the answer from any of the proposed answer, but by other way (such as in Ubuntu forums, Linux forums or other stack Exchange site or by your own research ) then you should write the answer, and accept it. This way, the future visitor will be benefited from your answer. Note that, you can accept your own answer after two days of submitting question.
And for the consequently closed feature, As far As I know, this is not possible. The question will be open for any future answers. Even, later answers can get more upvotes than the original accepted answer. The question is only closed if they do not comply with Ask Ubuntu policy as the FAQ indicates.