To use Reactor with your application you will need to create a ColdFusion data source and a mapping to a directory where Reactor generated objects will be written for your project.
For example, if I was working with a database named "Example," I would create a data source in ColdFusion for that database. I would probably name that data source "Example," though the name of the data source can be anything.
Additionally, I would probably have a directory named "data" where I would want Reactor to write files. To facilitate this I will need to create a mapping which points to the "data" directory. I would probably name this something like "/MyApplicationData". Once again, the actual mapping name is not important and can be changed without impacting your application.
When you create you Reactor.xml configuration file you will provide the data source name and the mapping to the data directory. For more information see the Reactor.xml Configuration File section.