It is not that simple a subject (or series of subjects).

You can do what you want with AutoText (in a global template) and AutoText Fields. This takes some thought and is not necessarily straightforward. Otherwise, you can store your variables in a separate document and use macros to pull them from that document into your destination documents or use Include fields (but those are at least as complex in implementation as is AutoText).

Greg's page on Repeating Data (Populating Multiple Like Fields) is the best compilation of other methods of which I am aware. It is not an easy read.

Bottom line:
Word is a Word processing program with a lot of extras built in. You are expecting it to get database program functions from it. I've been doing it for years (at least since 1993 when Microsoft told me it couldn't be done). I've been using AutoText to do this.