Categories are used to control the visibility of components in your drawing. Components automatically have categories assigned, but they can be added or removed. Similarly, when placing components in a drawing with multiple levels, objects are automatically assigned to a level.
Use the Levels tab in the Categorization dialog to see which level an object is assigned to or the change it to another level. You can access the Categorization dialog from the Tools drop-down menu or by right-clicking on a selected component and selecting Categorize from the context menu. You can also access it directly from the Architectural component tab by clicking Level categorization ...
Placing components on a level
A level will automatically be decided when placing a component. If you are placing an object in the 2D view, it will belong to the active level that is active. The active level will have a black outline around its name in the level buttons along the bottom of your drawing view. In this case, Level 2 is active:
If you are placing an object in the 3D view, the object will intuitively find the level you are hovering over. You will see it appear on the correct level, and once placed, it will be categorized to that level. Note that after placing on object on a level in 3D, that level now becomes active and is outlined in the level buttons at the bottom of your drawing view.
Moving components to a new level
The level a component is assigned to is indicated in the Levels tab with a checkmark. The check marks can be either gray or black. Gray checkmarks indicate the default, automatic level an object belongs to. Click any checkbox to add or remove a component from that level. This may be necessary when you have moved a component to a new level. Changing it visually in your drawing does not always change accordingly in the Categorization dialog.