All of the tools relating to the creation, editing and management of your 3D components can be found on the Modeling tools page, which is normally available as a tab at the bottom left of your screen next to the Drawing tab.
The Modeling tools tab is divided into two sections. The top section hosts the tools that relate to 3D components (including the relevant tools that are also accessible from the Drawing tab). The lower section lists all the components and component groups currently in the model - this is referred to as the Component Tree.
Click on an icon to learn more about it:
Creates a component that is the size of your job setup with a height of Zero.