Citykid,
I think JimLap jumped on you a bit harshly there, but it happens. In terms of a DM, I had one in OW class, I had one somewhere around dive 40, and again around dive 75. Those are the only DM's I've ever seen. The guy around dive 40 asked if we wanted tanks set up (I declined), asked if he could do anything (I was ok), he set the anchor and retrieved it, and that was it. I thought that was perfect! He did exactly what I needed to enjoy my dive. Of course we were about to drop to 105ft on a wreck, but hey... Second DM was new to DMing, did pretty much the same thnigs, but stayed on the boat the whole time. We had a nice chat during the surface interval. Again, a wreck dive, but this time the bottom was 212. We were only doing about 120-130 that day.
So what does a DM do? Seems to me like they set up the dive parameters and attempt to assist those that need help. I learned to dive without one, and honestly, am glad I did. The reliance some people seem to have on these people is astounding. I am not saying that necessarily about you, you're a new diver.
Best thing I can tell you is to get a dive briefing pre-dive, get the site and dive parameters explained to you, splash and have a good time. If a DM is there, terrific. If not, no big deal. I have yet to be around the type of DM that feels they need to run the show. I don't look forward to my first encounter with one.