Master page template

Hello everybody!
I’m gonna crazy to setup a page template that I can use later into more site pages with doing few modifications.

For example: if you offer your services in more than one area of your city and you’d like to plan to make a single page for each area, you’ll prepare a “master template” that you’ll customize each area name page.

When I tried to do this, I only saw the template with last modifications I made in the previous page.

Please help me! TIA and have a good weekend!