The Westminster Confession of Faith, The Westminster Larger Catechism and The Westminster Shorter Catechisms are documents carefully and thoughtfully written and compiled over many years by a council of theologians established by the English Parliament in 1643. These Standards summarize Biblical doctrines that the PCA (with a few modifications) holds to be the system of doctrine taught in the Holy Scriptures. Since the Bible itself is our only infallible rule of faith and practice these Westminster Standards are secondary and subject to the Bible.
The PCA Book of Church Order (BCO) sets forth principles and procedures relating to the governance of the Presbyterian Church in America, which are founded upon, and agreeable to, the Word of God. Jesus Christ has established His system of government, discipline and worship, all of which are either expressly set down in, or by good and necessary consequence inferred from, the Holy Scriptures. Therefore, the BCO, like the Westminster Standards is secondary and subject to the Holy Scriptures.
The PCA has many different committees and agencies: