The option to create a part catalog provides you a single place to define Part data (Part catalog) and then use these Parts in different BOMs.
To learn the basics and more about part catalogs, read the following articles:
By default, every user will have a Part catalog to store information about parts. You are able to create a Part directly from a BOM and store those in the same catalog OpenBOM automatically create for you.
This video shows you the work-flow in practice: