Templates for pages or regions?

Beginner here. Are the templates created in Perch for a portion of a web page, like a region? Or are they templates for an entire web page? If I make a home page for a 5-page site, and I want the index to be the template for the other 4 pages, is Perch capable of that? Or do I need to create the pages separately with my copy/paste my html template in my notepad++ editor to upload to the server? That's if it's from scratch.

What if it's a 12-page site all created with basic html and I want to make several text and image regions editable on each page for a client? What are the templates for? Regions? Or pages? Or can it be both? How do I make a region template for this client?