Have you seen and read Semantic Model | openHAB?
If so and are still confused have you seen and read A Deep Dive into the Semantic Model?
tl;dr: Everything in openHAB revolves around Items. The semantic model is defined using Items. A Location is a Group Item with a location tag applied. Equipment and Points are added to a Location by making it a member of that Group. The same things goes for Equipment and Points. These are Items that have Equipment or Point tags applied to them.