Special meetings can be called in accordance with provisions in your bylaws for calling special meetings. Whoever usually presides at your meetings would chair special meetings.
I think the questions have been answered in your other thread. Perhaps you could ask any follow up questions there.
Edited to add that the threads have now been combined.
The board may allow nonmembers of the board to attend board meetings. The board could also exclude nonmembers of the board at any time in these meetings.