On static sites (like blogs or documentation sites) a URL's path mirrors the server's filesystem hierarchy.
For example, if the website https://exampleblog.com had a static web server running in its /home directory, then a request to https://exampleblog.com/site/index.html would probably return the file located at /home/site/index.html.
But technically, this is just a convention. The server could be configured to return any file or data given that path.
Paths in URLs are essentially just another type of parameter that can be passed to the server when making a request. For dynamic sites and web applications, the path is often used to denote a specific resource or endpoint.
The Jello server uses URL paths to denote different "resources". For example,
/issues/projectsThe entire server is hosted at the path /v1/courses_rest_api/learn-http, so all requests must be prefixed with that path.