Configuration of Nimble when installed into a host application happens at two key points:
Values in DefaultNimbleConfig.groovy are all considered to be sensible defaults for most folks usage of Nimble, however all of these values an be overridden by simply redefining them in NimbleConfig.groovy a common use case for this is setting table names for domain objects to avoid clashes in your database of choice.
In addition to overriding values set in DefaultNimbleConfig.groovy there are many values in NimbleConfig.groovy that MUST be set for your application to function correctly. The install guide assists you in setting up a reasonable set of defaults for this file. Each component on Nimble such as the OpenID realm describes its config requirements in more detail.DefaultNimbleConfig.groovy is located at $home/.grails/<grails version>/projects/<project name>/plugins/nimble-<version>/grails-app/conf should you wish to review it. No changes should be made in this file.