When writing an application using the framework, you normally do not care about any of its components - except EditingContexts.
An EditingContext is the place where your objects live, i.e. where they are inserted, fetched, deleted, or updated. This important container holds your graph of objects as it gets changed, until the point where these changes are saved as a whole.
However, depending on the kind of applications you are developing, you will take different approaches. We'll see how this can be done, either in a pure-python application or within application servers like Zope or others. We suggest that you read the whole chapter, whatever your specific needs are: it explains how the framework reacts and how it can be used in standard situations.