The BI Manager plug-in essentially replaces the Business Report Manager and Stored Process Manager plug-ins. It supports the same functionality of the two older plug-ins, while providing additional functionality for copying content across repositories.
If you have the BI Manager plug-in, you should have also received an updated Intelligence Platform Administration Guide. I believe the BI Manager plug-in is discussed in there. Specific documentation on the BI Manager plug-in can also be found from within the plug-in.