QCop is a system for interacting between applications.
You can test channels from the GUI using qcoptest.
There are two methods: 1. From the command line, 2. From your application.
From the command line you enter qcop channel signal value, e.g.
qcop QPE/System 'setBacklight(int)' 0
From an application you use a QCopEnvelope object:
QCopEnvelope e(channelname, messagename); e << parameter1 << parameter2 << etc;