As said clicking the report button will take you to a new page where you can type a reason for the report (the box itself is small, but that is to discourage abuse, the actual amount of text you can enter is equal to that of a normal post). Though mods might not be around all the time so sometimes things might take a little whilst to get sorted; however we've a fairly decently sized and active team so lag times are pretty low.
Also note that the report command is also present in private messages - so again any abuse of that system can be quickly reported to us.
You can use this to report abusive comments, problems, spammers - basically anything where you feel a moderators attention is needed. We greatly encourage the use of this to report threads as moderation is a voluntary job and we don't see every thread so its easy for things to slip past our notice.
Further it helps in cases where you feel particular comments might be more abusive than we might have felt - again its giving us feedback on your views - we might not always agree, but it does not go unnoticed.
