If you want to know more about this tool, go to this post "Layout Custom Shelf"
To download it, click Layout Custom Shelf Download.
To install it in your Maya (and OS Windows) follow this steps:
1. Copy the "shelf_layout_custom.mel" file into this path:
C:\Users\UUUU\Documents\maya/XXXX/prefs/shelves *
* Replace in the path:
UUUU: Your user name
XXXX: Year of your Maya version (2017, 2018, 2019, etc...)
2. The path should be like this: C:\Users\Christian\Documents\maya\2018\prefs\shelves
3. To know how to install the tools "Studio Library" and "Main Scene Rig".