The chair runs the meeting. Under the Rules of Procedure the chair recognises speakers, times speeches, answers points, rules on motions, decides which amendments are debated, and counts the votes.
A committee has more than one chair, and the work is divided between them. One chair runs the debate. One chair handles logistics and messages. One chair handles amendments. See The chairing team.
Only one chair speaks to the house at a time. Chairs never contradict each other in public. Agree your approach with your co-chairs in advance, so delegates do not get different answers to the same question.
These are the chair's to make.
The reading time before debate. See Reading time.
The debate time, and for closed debate the time in favour and the time against. See
Which delegate is recognised, and in what order. See
Whether to allow a follow up point of information. See Follow up points.
Whether to allow a motion to extend debate time. See
Which amendments are debated. Prefer constructive amendments, such as adding a clause. Discourage
destructive ones. See Which amendments a chair entertains.
The chair never says whether the thing being voted on is good or bad.
A point of information to the chair is answered with facts and never with an opinion. See Point of information to the chair.
If you are unsure. A chair who tells the house what they think of a resolution will draw a point of order, and deserve it. If you catch yourself about to give an opinion, stop and state the procedural position instead.
The chair should repeat every point back to the house before answering it, because not everyone will have heard it.
Explain every decision to the whole house, not only to the delegate who raised it. A ruling that only one delegate understands has not been made properly.
Admit mistakes. Say "the chair stands corrected" and move on. Do not argue about it.
If you are unsure. Delegates sometimes invent points, or use the wrong words for a real one. Inventing a point is not allowed. Getting the words wrong is a mistake. Do not overrule someone because the wording was unfamiliar. Work out what they meant.
The chair applies the rules. The chair does not write them.
In MEDIMUN, a chair may not deviate from the Rules of Procedure. See Chairs may not deviate from the Rules of Procedure.
Once a delegate has moved an amendment, the chair cannot stop it being debated, unless there is a procedural mistake. The usual mistake is an amendment that refers to more than one clause. See Amendment of the first degree.
In MEDIMUN, the chair decides whether to accept motions through MediBook, and whether to accept speech requests through MediBook. That is the whole of the chair's discretion over MediBook. Everything else is required. See Chair MediBook obligations.
In MEDIMUN, the committee state is always declared in the MediBook control panel. Lobbying, debating, voting and so on. If the committee is on a break, the state is waiting. See Chair committee state.
SCREENSHOT: /medibook/sessions/22/committees/ga1/debate/control - the chair control panel with a speech running and the committee state visible
For chairing technique rather than procedure, see Chairing style and Common chairing mistakes.