For reference, see the docs
However, in href, you can either use an absolute URL, such as https://www.foo.com/bar.html or, relative, something like /bar.html, where / refers to the webserver root (but not webserver's system root), or, you can use bar.html which points to a file in the same directory level.
Basically you want to have a /hello/world link, it will point to www.foo.com/hello/world.
If you want it www.foo.com/hello/world to point at www.foo.com/bar/hello/world, you can either rewrite the URL on the server, or, redirect the users to www.foo.com/bar/hello/world
For URL rewriting, see your appropriate webserver docs