Office hours are generally from 6 to 8pm on Tuesday and Wednesday, always held in the student work area on the 8th floor. Two instructors will be present. They're completely optional, but can be extremely useful!
The format is informal: the instructors "on duty" hang out by the student work area, and if you get stuck, you can wander over and ask them a question, following the guidelines on asking for help. If everyone's having the same problem, the instructors may conduct an informal mini-lesson.