The QuickUI Catalog is evolving from a demonstration of controls to a library of controls intended for general reuse in other projects. This catalog can also serve as a design resource exploring different user interface components for consideration in your own projects.
You have several options, presented below, for using QuickUI controls in code. See the QuickUI tutorial, particularly the first section on "Using Controls", for the mechanics of how to actually use a control.
This is fine for just kicking the tires to watch some QuickUI controls in action.
If you want to pick and choose which catalog controls you want to use in a project, or if you want to build the catalog yourself, the source for the entire QuickUI catalog is maintained under the MIT license in the quickui-catalog repo on GitHub. Follow the instructions there for building.