Usenet Indexer. Similar to torrent trackers, indexers allow you to search for the media that you're looking for and provide you with a `.nzb` file similar to a `.torrent` file that you can use to download the files you want from the provider.

All you need to get started with Usenet is a Usenet service provider, an NZB index, and a Usenet client. Let's take a look these three things and get you up and running with Usenet. One final note on Usenet before we continue: Usenet can be used to download all sorts of stuff, and we're simply telling you how it works.

The 3 ways to search on Usenet – newsreader search, Usenet search engines and NZB index sites – let you do just that. So what are you waiting for, get downloading! RANK

This article will teach you how to search USENET for the files you want. You have several different options for searching USENET, some paid and some free, and we’ll give you an overview of them so that you can get the most out of your USENET subscription.

Search services have to use an index to make queries possible. Without an index the search would have to query every document each time a search is run. By using an index the search agent can speed up the queries: https://en.wikipedia.org/wiki/Search_engine_indexing.