Just what do moderators do?
We handle flags.
The main distinction between a regular high-rep user and a moderator is that all posts and comments on the site that are flagged go to us. We have a special flag menu that you can consider an extension of the review queue concept. Flagged posts show up there, grouped by question and with several available actions to process flags from that screen or to jump to the post or context (like a comment thread) for a flag. Every flag you submit will eventually reach a moderator who looks at the post or comment you flagged.
We see the flag reason, we see the question, answer or comment that was flagged and we see the author of both the flag and the post. We will then take action based on the nature of the flag. If we disagree with the flag we decline it. If we don't we usually take some action on the post but can also do nothing beyond marking the flag as helpful. That's typically reserved for good-faith flags that don't require a particular action. Note that there are also automatic flags when posts hit a certain number of answers or comments.
The usual actions we take, broadly in descending order of frequency, are:
- deleting obsolete comments
- deleting inappropriate comments
- moving comments to chat
- protecting questions (preventing answers from new users)
- removing questions from the Hot Network Questions
- converting answers to comments
- deleting answers
- deleting questions
- contacting users
- suspending users
- deleting/destroying users
- adding post notices
Most but not all of these are sparked by flags. Some of the most time-consuming activities happen outside the flags and relate to handling problematic users. Usually that means communicating with users privately (through site tools) to address observed patterns of behaviour. This private communication includes potentially suspending users for a certain amount of time.
Another activity which I will not describe in detail for obvious reasons concerns detecting and dealing with abusive users, i.e. trolls. This will typically involve coordinating with fellow moderators before deciding on a particular action. We have a private chat room for that purpose.
Beyond that, we also engage the Community Team in rare cases. Typically that's on behalf of users. About once a year it's to arrange an election. :)
As mentioned by MisterPositive in his excellent answer, we also typically keep an eye on the Workplace chatroom. Long gone are the days when we were able to read the entire chat but I like to keep an eye on it as it helps to get an idea of community sentiment. There was a time where the chatroom required some occasional moderation as well but I get the impression the room has stabilised and now champions the same standard of professionalism we strive for on the main site.
Since it has come up before and some numbers were already posted in meta and chat over the years, I'll share some ball-park statistics on our combined activities. Currently the moderation team will on average and per month:
- handle 250 flags
- delete 1500 comments (vast majority done in batch)
- delete 30 posts
- contact a handful of users privately
Please note that these numbers are indicative only.
How much time per day does it take?
This varies from moderator to moderator. Apart from Stack Overflow, Stack Exchange sites do not enforce a particular level of activity. Anyone who opts to run is expected to be reasonably active on the site but there are no real rules or set expectations. I would say that at a minimum, you'd be expected to spend about 5 minutes on the site handling flags a few days a week. Workload varies based on site activity and other moderator activity. After the last election the new moderators basically handled just about every flag between the two of them before the rest of us got to them, leaving only our Australian moderator some work due to the timezone.
Just for reference: we've had moderators on the site who were no longer really considered active (I would be one of them) but their diamond was not revoked over it. It did spark new elections but speaking personally there is real value in having experienced moderators around to chime in on the chatroom on important topics even if they don't handle much of the day-to-day.