A doctrine is a well-defined belief. It can be held rigidly in which case it is said to be dogma.
Christian doctrine is the collection of beliefs that have been held by Christians, in general, in various cultures and times in history.
Doctrine can be fundamental to Christianity itself, in which case it is held by all Christians. This fundamental, non-negotiable group of beliefs can be called essential doctrine, or Orthodoxy.
Another term used to describe the core defining doctrines of the Christian faith is The Great Tradition.
Different types of Christians can hold many other (nonessential) beliefs in many different ways that disagree with one another and can cause division. Since doctrine is based on revelation it is a summary of what we know about God. Of course, since so many nonessential concepts are variously interpreted it is important to compare the different interpretations of a Bible passage held by different Christians in order for a person to decide what they believe. Nevertheless, since formation of belief is the product of the corporate experience and wisdom of Christians it is relatively objective compared with a single individual personal experience of God.
One of the current debates in Christianity revolves around doctrine. Since the history of Christianity abounds with people who have had good doctrine but bad character it has recently been suggested that doctrine be minimized in importance. A Christ like spirit, with humility, forgiveness and a zeal for social justice has thus been promoted as the mark of a Christian. Doctrinal correctness, in this scheme, is minimized.
The price to pay for minimizing doctrine, however, is often a neglect of even essential doctrine. The uniqueness of Jesus can be lost, and within a short time His message is diluted into an ethical system that lacks the power of conversion and new life.
See also Knowing God.
A safe path at this time would be to strive for both: a good understanding of Jesus as well as personal experience with Him.