If you are browsing a self-hosted or public Spotweb instance (like NZBStars), you can download NZBs manually:

A Usenet client like SABnzbd or NZBGet reads that NZB and pulls the actual data from your Usenet provider. 2. Manual NZB Downloads

Downloading through Spotweb generally follows a three-step process:

You download a small NZB file from Spotweb, which acts as a pointer for your downloader.