Drupal 8

Drupal 8 uses a display type (feed) in views to provide feed pages, like the /rss.xml feed link. This view does not use the rss form settings located in admin/config/services/rss-publishing, which is confusing for users. There is an issue in progress to remove the admin/config/services/rss-publishing form from D8 core: #2409413: Remove fields that do nothing from the "RSS publishing" settings form

Drupal 7

In Drupal 7, core node module provides basic RSS publishing for content. An RSS feed is generated at /rss.xml. By default, the RSS feed will take the 10 most recently created pieces of content promoted to the front page and respect node access grants to ensure that users only see RSS feed items they are eligible to see.

Basic configuration

The admin/config/services/rss-publishing page may be used to add a description to the RSS feed and change the number of pieces of content displayed in the feed.

Adding fields to the RSS feed

If fields attached to content are desired to be attached to the feed as well, these may be configured on the manage display page for the content type. The "Custom display settings" dropdown should be opened and the RSS view mode checked.

This will add a new secondary tab to allow specific fields to be added for just RSS view modes.