Adding on to what Monica said, when you go to post a comment on a question you see the following:
The comments which Monica deleted there did not ask for more information nor suggest improvements to the question. Some of them were sort of answers, but the majority were a discussion tangentially related to the question.
There is a lengthy FAQ about comments here. I would encourage you to read the information page on comments, too, specifically:
When shouldn't I comment?
Comments are not recommended for any of the following:
Suggesting corrections that don't fundamentally change the meaning of
the post; instead, make or suggest an edit;
Answering a question or providing an alternate solution to an existing
answer; instead, post an actual answer (or edit to expand an existing
Compliments which do not add new information ("+1, great answer!");
instead, up-vote it and pay it forward;
Criticisms which do not add anything constructive ("-1, see previous
comments you scallywag!"); instead, down-vote (and provide or up-vote
a better answer if appropriate);
Secondary discussion or debating a controversial point; please use
Discussion of community behavior or site policies; please use meta
Hopefully this helps!