Open spaces are a way for people to come together to talk about topics, ideas or whatever they want. Any subject that two or more attendees want to talk about is a candidate for an Open Space.
It's pretty easy: just show up :)
During PyCon, there will be an Open Space board somewhere near the registration desk. The board acts as a time table for all the Open Spaces, so you know where and when to go for the Open Spaces you're interested in. If a topic is not listed yet, find an open time slot and add it!
The Open Spaces are in a set of of dedicated rooms(2nd floor) during all two of the conference days (Saturday and Sunday).
There will be an Sticky Note near the Open Space Board. Just fill in the name and a short description of your Open space, and then pin your note on the Open Space board in the room and time slot you want.