Hi Jose,
the "Layout Manager" property is intended for you to choose whether you want to organize the contents of your page in a standard HTML table (Custom Grid option) or in a responsive and flexible way using the 960 Grid System, which is implemented by the Grid System option.
If you want to use in your project the Boostrap Style you downloaded from the WebRatio Store you need to apply the Bootstrap Style to the project itself.
You can refer to this online lesson
http://www.webratio.com/learn/learningobject/choose-and-apply-style
which shows you the procedure to do such a thing.