At any time, you can open Spamfire and review the decisions it makes. From time to time, and especially when you first start using Spamfire, Spamfire will make mistakes. It will let messages through that should have been stopped, and it will stop messages that should have been let through.
When this happens, you can correct the decision. When you change a message from spam to good, you will be able to receive the message in your email program. See How to Correct Decisions.
When you make a correction, it automatically trains the Spamfire Bayesian filter so it can be more accurate in the future. After you train a few dozen messages, Spamfire will become very accurate.
Spamfire can even train itself.
You may see a brand new spam message, one that Spamfire is unable to recognize. Spamfire will give it a spam score of 50. Because 50 means "unknown", Spamfire will release the message to your email program (you can customize this behavior). You can select this message in the Spamfire Mail window and click the Is Spam button. The next time you receive this message, it will have a higher score. Spamfire will recognize it as spam and stop it from reaching your email program.