311 is about getting better customer service from your city or other local governance. You call, or Twitter, use the web, or whatever you like, then you get results.
Those results might be anywhere from getting the garbage picked up, getting a pothole fixed, or working through a permits process. Mundane stuff, but we live most of our lives in the mundane (hopefully.)
One big step regarding that is a standardized way for software to interface with gov't agencies, so that it all works the same way, that good software written in one city might just work with another. That's what the "open" part of Open311 means.
San Francisco city gov't is serious about getting stuff done, and is a big part of this, as the Mayor says in the YouTube clip: