Ordination to priestly ranks is always done during the Divine Liturgy. It should always be individual; no more than one ordination to each order should be done per liturgy.
The authority of ordination is for the bishop and higher ranks only. An ordination of a new bishop should be done by at least two bishops. Deacon, priest and bishop ordinations are done by "Laying on of Hands" (Greek: Cheirotonia) - Apostolic Succession.
Despite the fact that ordination can only be done with bishop(s) laying on of hands, it must also be approved by those present. So the whole congregation expresses its consent with shouts of "Axios!" (Worthy!) at certain times during the ordination service.
In the Orthodox Church there are three main priestly ranks:
A - Deacon: servant.
B - Archdeacon.
A - A priest: who can practice all sacraments except ordination.
B - Archpriest.
C - Archimandrite: The head of a group or the abbot. Originally a monk in charge of the spiritual administration for several monasteries, or an abbot of particular importance. The title is used today as an honorary rank for the special hieromonk.
A - Bishop: a Greek word meaning headmaster or overseer.
B - Metropolitan (Bishop): The word is derived from the word Metropolis meaning the Mother City, so the metropolitan is the bishop of the Mother City. It is a promotion in his Episcopal ranks.
C - Patriarch (Archbishop): the ‘Patriarch' word is driven from a Greek phrase meaning the leader (archon) of fathers (patria).
There are also submicron ranks: sub-deacon and the reader.
Orthodox priests are divided into two categories: married and unmarried priests. Those wishing to join priesthood should choose so before ordination. It is not allowed to marry afterwards. Those who wish to marry should marry before becoming deacons. While those who do not want to marry should become monks before their ordination. If a priest becomes a widowed, he is not allowed to remarry.