How does the browser know what resources to cache? code example

Example: what is a browser cache

When you visit a website, your browser takes pieces of
the page and stores them on your computer's hard drive.
Some of the assets your browser will store are:

Images - logos, pictures, backgrounds, etc.
HTML
CSS
JavaScript
In short, browsers typically cache what are known as 
"static assets" - parts of a website that do not change
from visit to visit.