Chapter 7 is an introduction to 3D modeling. 3D modelling is important in Vectorworks (as you will notice from chapter 2). Chapter 7 covered techniques like extrusions, add solid, subtract solid and so on. You can use those techniques to create the bracket showing here.
How did you get on? If you found this difficult, go back to chapter 7 and go through exercise again. These 3D tools and commands are very useful and will be the basis of your 3D modelling work.
If you do not have the Vectorworks Essentials tutorial manual but you would like to learn Vectorworks I strongly suggest that you purchase this manual. Here is a link that you can use to find the manual. http://www.vectorworks.net/training/guides.php