A morally-acceptable duel would start with the challenger issuing a traditional, public, personal grievance, based on an insult, directly to the single person who offended the challenger.
The challenged person had the choice of a public apology or other restitution, or choosing the weapons for the duel. The challenger would then propose a place for the "field of honour". The challenged man had to either accept the site or propose an alternate. The location had to be a place where the opponents could duel without being arrested. It was common for the constables to set aside such places and times and spread the information, so "honest people can avoid patrolled places."
At the field of honor, each side would bring a doctor and seconds. The seconds would try to reconcile the parties by acting as go-betweens to attempt to settle the dispute with an apology or restitution. If reconciliation succeeded, all parties considered the dispute to be honorably settled, and went home.
Each side would have at least one second; three was the traditional number.
If one party failed to appear, he was accounted a coward. The appearing party would win by default. The seconds and sometimes the doctor would bear witness of the cowardice.
If reconciliation failed, the seconds would help their friend prepare for the duel, and keep alert for cheating and the authorities. Cheaters would be shot, usually out of hand. Honorable seconds sometimes shot their own friend if they found him cheating.
Swords were the typical weapon of the time, although it was not uncommon for guns and more unusual items to be selected.
The two parties would start on opposite sides of a square twenty paces wide. Usually the square was marked at the corners with dropped handkerchiefs. Leaving the square was accounted cowardice.
The opponents agreed to duel to an agreed condition. While many modern accounts dwell heavily on "first blood" as the condition, manuals of honor from the day universally deride the practice as dishonorable and unmanly. Far more common was a duel until either one party was physically unable to fight or the physician called a halt. While explicit duels to the death were rare, many duels ended in death of one or both combatants because of the wounds sustained.
When the condition was achieved, the matter was considered settled with the winner proving his point and the loser keeping his reputation for courage.