LunaSea supports any indexer that supports the Newznab API specification. Most modern indexers (including NZBHydra2) are fully compliant with this specification, and compatible with LunaSea.
Your personal display name for the indexer. The display name can be anything, but indexers are displayed in alphabetical order and the display name you choose will determine where it lands in your list of indexers.
This is the API host from the indexer. Do not confused this with the homepage for the indexer! Some indexers use the same URL, but many indexers will use a separate URL (commonly https://api.indexer.com).
If your indexer can and has been added to Lidarr, Radarr, or Sonarr, you can simply copy the URL from the indexer configuration page within their settings.
Your API key that is typically available in the dashboard of the indexer or received by email when originally signing up for the indexer.
If you are unable to find your API key, consider contacting the administrators of the indexer to get help! The LunaSea developer and community users can try to help, but we cannot guarantee support if nobody has access to said indexer.
Custom headers allows users to attach custom request headers to each API call that is made. This is typically an advanced feature, and is not necessary for most public indexers.