A quorum can be described as the minimum number of voting members who must be present at a meeting to do business for an organization, whether non-profit or otherwise.
If people are outside the meeting room just moving about, the Sergeant-at-Arms should let them know that the meeting is about to begin so they can all take their seats.
Then at the time of the meeting, the group's Chair is responsible for deciding if the quorum is there or not. Once a quorum is confirmed, the Chair can legally call the meeting to order.
If the quorum is absent
However, if the quorum is not present, the assembly can deal with the situation by taking several steps. They can either have a recess, adjourn the meeting, fix the time for which to adjourn or obtain a quorum through various measures.
Please note that if the assembly acts informally without the quorum being present, they do so in breech of the rules/bylaws governing the body.