Assuming there is a Video Crew who have taken care of the preparations, volunteering to help them is very easy. The system is designed to be used by people with no experience in anything at all.
Just let the Video Crew leader know you are interested, and show up on time, generally 30-60 min before showtime. The sooner you let them know the better. months before is great, but last minute is fine too. the only reason someone will be turned away is when there are way too many on the crew. But even in that case there will be people with nothing to do who will be happy to show you how things work so that you have a head start on the next event.
There are a few roles, often 1 person will cover more than one role. Ideally you want to be familiar with all of them and practice on the ones you are interested in. This takes about 10-90 minutes of orientation. You will get pointers like:
pay attention to your job - If you are an attendee of the event, you may find yourself focusing on the event and forget about the recording. If you do a good job then you and everyone else will have a good video to watch later.
There are typically people ready to help if you have problems. At a large event, there will be veterans who's top priority will be to help out the rookies. (example 2 room event: there will be 4 rookies running the equipment and 1 or 2 veterans available to help. This takes more people and the quality suffers a bit because there will be more rookie mistakes, but it ensurers there will always be someone to help.)
Camera
resist the urge to zoom and pan. It is fun to do, but not fun to watch.
If the presenter is moving all over the place, zoom out so that they move back and forth in the frame. This will let the view experience the presenters characteristics, which is the point of shooting the video and not just audio.
if they are doing laps from one edge of the stage to the other, zooming out to about 1/2 the stage, and shift (slowly) back and forth between the 2 sides.
If the dvswitch operator is doing PnP with the slides in the upper corner, you want the speaker centered in the remaining area. This takes a bit of communication between you and the dvswitch operator.
relax. you probably are not going to destroy anything, the dvswitch operator can always cut away from your stream if it really a problem.
Try to spend 10 minutes practicing with the equipment before the event starts. Ideally days before, not the day of, but anything helps. Being nervous because you are not familiar with the system is one of the bigger problems - it doesn't take much to get an adequate comfort level.
DVSwitch
Watch videos where DVSwitch was used. seeing it used poorly is probably the best way to learn what is poor.
Practice. Spend a few minutes with the test patterns, use the few minutes before the talk starts to warm up.
Sound Board
no clipping - the worst thing that can happen is the level is so high that the electronics can't handle it and the curvy sine wave gets smashed flat. This causes the result to pop, which is very distracting and difficult/impossible to fix.
consistent audio - it is very annoying to watch a video where the audio level keeps changing so much that you feel the need to adjust the playback volume. or have to strain to listen to soft parts and then have your brain blasted by sudden ?loudness?.
In Fantasy Land the presenter speaks clearly into the mic, with a consistent ?volume? and proper and consistent distance from the mic. When someone in the audience has something to say, they walk over to the audience mic and speak with the same consistency as all the other audience members. There will be no interfering noises, like air conditioners, silverware clanking on plates, alien invasions, etc. This does not happen. Perhaps the trickiest part of the process: getting a feel for the behavior of the presenters and audience and adapting to it.
Coach the presenter and beg the audience to use the mic, but disrupt the event too much. Get each presenter do do a sound check, perhaps have some text for them to read.
When there is more than about 30 audience members, a persons voice is typically not loud enough for everyone to hear, so a PA system is used. People talk into the mic, and if there is a problem (mic off, not talking into it, etc) the person talking notices, or someone in the audience will cause a fuss "We can't hear you!" and the problem will be dealt with. For a small group where everyone that does not use a PA system, that checks n balance does not exist. Now the person running the sound board will be the only one that knows how it sounds, and must be the one to blurt out "talk into the mic."
The point of a ?room mic? (condenser, ambient noise) is to pick up things that the other mics don't: typically comments blurted out from the audience, applause, the presenter not talking into the mic. When there is something worth recording, you bring the level up so that you get a good recording. When the presenter is speaking, keep it low but not off; a little bit of noise is OK, it ensures you pick up everything that needs to be without making it hard to hear the presenter. Hearing the presenter clearly is much more important than hearing the audience blurts, but there should be some chance of hearing them even if it isn't clear. As a listener, just being queued in that someone is blurting, and maybe being able to understand 1/2 of it is pretty good. The presenters response will likely cover most of the information that needs to be conveyed to the listener.