Bayes analysis is the learning system built into CanIt. There is a brief description of the system in the User Guide in section "9.1 Introduction to Bayesian Filtering".
The second area is the voting links that can be placed at the end of any incoming message. This is controlled by the setting "S-2500 Add links to messages to train Bayesian analyzer" on the Preferences->Quarantine Settings of the webui. Upon installation this is set to Inline by default which means the voting links will appear on incoming messages. Clicking on a link will allow you to do the Bayes voting without having to long into the CanIt webui.
One point worth emphasis is that care should be taken in voting messages. If messages are incorrectly marked as spam or non-spam this can "poison" the Bayes database and degrade the effectiveness of the analyzer. You are better to delete or allow a message to expire than voting it incorrectly.
For more specific detail consult either the User Guide or the Administrators Guide documentation.