Hotbars are special kinds of Inventory Displays. They extend that base class to add key binding shortcuts to activate an action (use or equip) on the items in it. A good example of a use case is the potion hotbar in Diablo 2. In the PixelRogue demo provided with the asset, there is an example of a Bomb hotbar. All bombs you pickup in the levels will go stack into that inventory, and you can detonate them using space (or joystick button 0).
Creating a hotbar is exactly the same as creating an InventoryDisplay, except you’ll need to add an InventoryHotbar component instead of an InventoryDisplay one.