OK, this is one of my favorite questions I’ve gotten so far. This will just be fairly brief, but I hope it will be helpful.
The Book of Common Prayer is not Scripture, although the prayers, canticles and versicles/responses are based on Scripture verses. The BCP also contains the full text of the Psalms, which are read or sung together by the congregation.
It is also not meant to confine us in how we pray, either, or demand that it be the only source of prayers that are used. Rather, it helps provide a perspective on how Christians have worshiped through the centuries, and offers an order of service that allows everyone present the opportunity to fully take part.
It gets its title from the fact that the prayers and liturgies (Masses and other services) were for everyone (i.e. the common woman or man), written in the English language. The first BCP, published in 1549 after the Church of England’s break from Papal authority, was something very different for its time.
Over the years, the various Anglican communities outside of England have adopted their own BCP versions to suit local needs and culture. Updates to the different versions have included modernized language and the addition of liturgies suitable for localized needs.
Some of the most well-known editions of the Prayer Book include: The 1979 Book of Common Prayer (US), the 1928 Prayer Book (US), the 1662 Prayer Book (Church of England) and the New Zealand Prayer Book (the latter two aren’t in the public domain).