As soon as someone sets out to read the Bible, the next logical step is to interpret it and formulate doctrine. The Bible does not read itself and it needs to be understood as a collective unit. Unfortunately even the best of Christians can misinterpret the Bible. That's why the Holy Spirit has given various gifts to the Church and those gifts, ie. teaching, wisdom, etc. are to be used collectively, as a body. The Bible did not just "fall out of the sky." It has it's own history.
Someone once said, "Before we come to the Word of God in Genesis 1:1 we come to the "word of the church" in the table of contents of the Bible." And my point? Those who boldly proclaim, "No creed but the Bible," unwittingly hold to at least a couple of creeds:
1. The creed which says, "No creed but the Bible." (Try though you might, you will not find it in there! Neither will you find "God helps those who help themselves," nor "Cleanliness is next to godliness."
2. The Table of Contents in the Bible is itself a creed. Again, the Bible did not just fall out of the sky. Somewhere down through the course of history we're trusting that when someone acknowledged the 66 books of the Bible were indeed the Word of God, they got it right!
The Westminster Confession of Faith is not on the same level of authority as The Bible and neither are our moms and dads. However this does not negate that creeds such as The Apostle's, The Nicene, Etc. along with the Three Forms of Unity, and others carry authority. When a parent says, "Eat your peas, Junior!" that's authoritative, and God supports that kind of authority. The creeds and confessions are authoritative as long as they correctly interpret and stand under the Bible as secondary authorities.
If you are interpreting the Bible ONLY as an individual, you are not holding to the doctrine of sola Scriptura but rather SOLO Scriptura.