How does nonmarital property enter into this distribution?

It is separate, in that it cannot be divided the way marital property can. "Separate" does not mean that it is ignored, however.

If your wife, for example, has a great deal of nonmarital property, the court may award you more of the marital property, so that both you and your wife are in an equitable position. If the judge can leave both parties in a comfortable position, he or she usually will try to do so. This is why equitable means fair, not equal.