search – SharePoint 2019 ON PREMISE – How to create managed property

I am not sure on the flow of how to go about making a searchable managed property.

I need to create a property that allows numbering sequence to enable a user to set the priority (1-1000) on news items.

Currently there is not enough choice under the highlighted content.
I need an A-Z on how to do this and enable it the managed content to be mapped / crawled.
Help always appreciated.