there’s a new user tutorial. Also, please be aware of the fact that no one here knows your setup and answers to your questions can only be as precise as the input you’re willing to share.
There are so called “add-ons” for openHAB, you can find them here. So for your first question; if you have a KNX-wiring (?) and want to switch on/off lights (?) with openHAB, you’d need the KNX-binding. Any KNX-certified/compatible switch-brand is your friend in that case.