OpenHAB supports a lot of different "bindings", i.e., Hardware and Protocol solutions implemented by different companies. I started my home automation project with the Homematic binding. There are two tutorials I follow (german only):
The first one was really easy to follow and worked straight away. I had to restart the OpenHAB service, though, which wasn't mentioned in the documentation.
For the second tutorial I ordered the window sensor and the heating control as mentioned in the tutorial. They haven't arrived yet, so I will post again when they arrive.