Using Fields and Creating templates

I am trying to create a set of templates for multiple instances Project Management (Prince2) documents. I want to use fields and variables to collect global information relevant to each project like using an input field to collect the name of the project, the type of document, the names of each section in the document. I want to enter the date once and use it in multiple places. Having difficulty in understanding how to do this.

One can learn a lot from the templates on https://extensions.libreoffice.org
When I search for “fields” with tag “Writer”, I get several CV templates and Letter with headers and footer » Libreoffice Extensions using input fields.