The source files have the following setup. There will be additional components and pages that will vary depending on the theme.
src/assets/ - Images and other assets
src/components/ - Individual components used throughout the site
src/config/ - Configuration files for site data
src/content/ - Content collections
src/js/ - JS utility functions
src/layouts/ - Astro layouts, used for multiple pages
src/pages/ - Pages / routes of the site. If you see something like
[slug].astro, that means it is a dynamic route, and likely pulled from content collections.
src/styles/ - Global styles
There is a code tree like this included in the
README.md of each theme.