The plugin is a backend for QtContacts, therefore you probably want to read the Qt Mobility documentation first.
QtContacts-Tracker implements a few extensions to the mobility API:
Those classes are in the qtcontacts-extensions-tracker library.
There is also an interface to contactsd's garbage collection plugin: QctGarbageCollector
Finally, you can pass a variety of parameter when creating the QContactManager, see the QContactTrackerEngineParameters documentation.