On the left side of your workspace is the Scene List. This is a visual representation of how all the objects in your creation are organized, and how they effect each other. Keep reading to learn about Union, Group and Subtraction as well.
https://www.youtube.com/watch?v=3i_26S4U35c
In this lesson:
With more complex creations it can be helpful to lock or hide some objects or unions, to keep the focus on the part of your model that you are currently working on. This is easily done in the scene list, and can be toggled on or off whenever you like.
The Object tab is a quick way to add a primitive or community model.