Dear brothers and sisters in Christ —
The Vesperal Service in the Orthodox Church can have four different orders: Daily Vespers, Lenten Vespers, Paschal Vespers,and Great Vespers. In addition, Great Vespers can be served in conjunction with Matins, to form the All-night Vigil. The booklet you hold in your hands contains the fixed parts of the service of Great Vespers and the 9th hour, and is intended for use when Great Vespers is served by itself on Saturday evening and the eve of feast days, with or without the Litia.
When served by itself, Great Vespers is usually preceded by the 9th hour. The hours of prayer are short, read (not sung) services, which correspond roughly to dawn (1st hour), morning (3rd hour), midday (6th hour), and mid-afternoon (9th hour), comprised of the opening prayers, 3 psalms, hymns, and prayers. These “canonical hours of prayer” have Biblical roots, and, along with Matins, Vespers, and Compline are a manifestation of the “sanctification of time”. It is normal to “aggregate” the hours to the nearest “main” service: the 1st hour following Matins, the 3rd and 6th hours preceding the Liturgy, and the 9th hour preceding Vespers. The 9th hour is the last service of the liturgical day (e.g., the 9th hour on Saturday afternoon is the last service of Saturday, and so we would read the festal or daily tropar and kondak for Saturday during the 9th hour), and Vespers is the first service of the new day (e.g., Vespers on Saturday evening is the first service of Sunday, so all the stykhyry, hymns, the dismissal, etc., are all for Sunday).
Depending on the local parish practice and the particular solemnity of the day or feast being celebrated, certain portions of the service will change.