Those are called the columns, have you tried reading 960.gs to learn more about it? Here is a demo. You can even view slides.
Your design is based on those columns and there are different options and columns such as 12 column, 24 column, etc. etc. A good read about it is over at code tuts called Mastering the 960 Grid System that explains how to use them.
If you look at the 960 grid website there are example sites that you can click the show grid button and get an understanding of how the site was designed based on the columns:
If you're starting out I would encourage you to look into developing in the browser with something like Bootstrap or Foundation because your design would not be responsive.
If you are looking for desktop only I would look into something bigger than 960 such as 1080.gs
After clicking the big download button.
- Open the file
- Go to
Window -> Layers
Double click the
12 Grid layer:
If you're trying to use CC to open the latest file per the download it says that it is for up to CS5 and its a template file:
In CC go to the tab
Pages and double click the
A-Master white sheet to edit the grid: