If you want to connect two landline phones in the house, do you simply have to buy two of these Gigaset e560s and can you then connect them yourself as a layman?
Exactly. When buying, make sure that one of the devices has a base station. This is the part into which you plug the connection cable to your telecoms provider into the socket. All other devices are based on this one. It may make sense to buy additional devices in a specialised shop. Online shops often only offer the basic version.