What is Layout Library and where can you find it?
Layout Library has been compiled by our creative genius' to provide you with free designs that you can copy and paste into your page builder for you to customize. You can find it by going to: https://layouts.siteglide.com/
Layout Library is what you see on the front-end. It consists of templates for you to replicate onto your Site.
What is Design System?
Design System is everything that you don't see on the front end of the layout library as well within your site when you have installed the Design System module. It is a collection of reusable components, guided by clear standards that can be assembled to build a variety of aspects.
What is the difference between the two?
Layout Library are the designs that you see; and the Design System is what is applied to the layouts as well to your Site to enable it to be scalable and replicated with ease using Bootstrap 4.