This is a quick world-of-science demystification post.
I get the feeling that what non-scientists think science conferences are like and what they're actually like don't quite overlap as much as they probably should. The TV show Big Bang Theory doesn't help. Brawls don't tend to break out and people are rarely drunk on stage, even students.
Of course, I'm writing this from an astrophysics conference and I've never been to a biological conference, for example (though I have been to a general physics one), so it's entirely possible that biologists do brawl... But I doubt it.
Edit: a biology friend on FaceBook informs me that they don't brawl either. She also reminded me that I should mention the after-hours drinking. No one's drunk on stage, but in the evenings, especially after the conference dinner, drinking late into the night is not unusual.
The basic format is a series of talks in a lecture theatre. There will usually be some longer invited talks and then the majority of talks that people have to apply for. You put in for a talk by submitting an abstract (online) and, if the organisers think your talk will be interesting and if it fits into the program (and if you have some modicum of credibility rather than being a walk-in off the street), then you will get a talk.
If it's a large conference, there might be streams where talks on different topics take place simultaneously in different rooms.
Usually, there will also be a bunch of people who present posters. These people will often (but not exclusively) be students or other researchers who don't have quite enough new material to fill out an entire talk. People who don't get to do a talk, but want to, will usually make a poster instead. Posters will be displayed in some room or corridor and other attendees will wander around during tea and lunch breaks, viewing said posters and talking to their presenters. Sometimes there might be something called a sparkler session (or at least, that's what we call it at Australian astro conferences) where poster presenters get 30 to tell the audience why they should bother looking at their posters.
Overall, the most exciting things that happen at scientific conferences are heated discussions about science, technological malfunctions and bad puns. No brawling, d'you hear that, Big Bang Theory?