Components are essentially supergroups. Like a group, making an object a component provides a protective bubble around the object. A key difference is that you can make a copy of a component, and when you make a change to that component the change will be reflected on all the copies of that component. This makes it much easier when working with a model that has repetitive pieces (like a dining room with 8 chairs).
Tags and Entities are both found in the Default Tray on Windows or in the Window menu on Mac.
Tags control the visibility of an object/entity. You can give multiple entities the same tag (i.e., “roof,” “outer walls, ” or “second floor”), and click the eye icon in the Tags tray to make everything with that tag invisible. This can make it easier to work inside of a model.
Each object in your model is an entity. The Entity Info tray gives you more information about each entity, like the square footage.