After installing the application, you can add documents in __INSTALL_DIR__ (or the corresponding path you choosed).
h5ai doesn't allow to edit or upload new documents directly from the web browser. But you can imagine coupling the folder __INSTALL_DIR__ to Nextcloud or some sort of FTP to allow some users to upload content, and use h5ai as a public read-only interface.
The main configuration file is _h5ai/private/conf/options.json. You might want to change some of the documented settings. But there are some more files in _h5ai/private/conf you might have a look at.