When to coment and when to post an answer?

I am confused as to what exactly constitutes a comment and what constitutes an answer?

For example, when the editorials for a contest are published, they are published in the form of a question and answer combined as a question. Instead, shouldn’t CodeChef be posting the answer separately? Otherwise this leaves no use of the ‘answer’ field. It is then solely used to post indivisual users’ solutions and/or their doubts (as to why their code isn’t working, along with the whole code, or some other question itself describing their doubt.

Also it seems a very minority of the users use comments appropriately. As an example, see this (what he should have done is to post it as a comment to the original question).

For a normal question, a comment should be used when you want to clarify something related to the question or you have just a small suggestion that does not actually answer the question.In case of editorials some users do post unnecessary things as answers instead of comments. That is why certain users are given the power to convert comments to answers. I do not think that this is that much of a big issue that it needs to be discussed here so i am closing this question.

If “certain users are given the power to convert comments to answers”, then who watches those who post “unnecessary things as answers instead of comments”?