By default, objects from the asset library already have a Visual Node, which controls the visual properties of the object including it's 3D model & visual materials. Some objects may also have a Physical Node that define physical properties.
Objects can hold up to 9 nodes (not including Visual & Object Nodes).
Each Node has editable parameters that can be accessed via the Advanced Details panel when an object is selected.
Add new Nodes to an object from the ➕ button, and remove them via the 🗑️ button.
Add new Nodes independent from any objects via the Logic Menu found at the bottom of the screen.
What Nodes are available will depend on how the logic menu is accessed. For example the Node Character Animation can only be used on specific objects so will only appear as an option in the logic menu when tapping the ➕ icon in the advanced details panel of one of those objects.