Hello Willi,
whats described on page 57 is the “light” mode to connect two HM devices if you don’t own a CCU. As far as I know once HM devices are connected to a CCU (Homegear in your case) the “light” way of connecting them will not work any longer (so you will not get them connected to OH anymore).
You will either need to use the configurator software from eq3 (I’ve had no luck with it) mentioned above that connects to Homegear on the PI or install a full CCU3 image on your PI. RaspberryMatic is the easiest way but does not allow to run OpenHab on the same PI but there are other distributions (piVCCU?) which can be installed side by side with OH. With a full CCU3 installation you will be able to use its web interface to do the coupling.
Homegear also allows you to run PHP scripts to control every aspect of the connected devices. It should be possible to create the connection in this way too, but this will require deep knowledge of the protocol.
So my conclusion: try to install RaspberryMatic on a separate Pi (which has the HM-MOD-RPI-PCB module attached) and use this as the CCU instead of Homegear. This is the easiest solution for a beginner I think.
PS: don’t forget to unpair/disconnect your devices from Homegear before going this step. This is important because they will refuse any connections if they are still paired and there is no way to reset the pairing at the device (for security reasons).