Answer 1. News feeds allow us to see when websites have added new content. We can get the latest headlines and video in one place, as soon as it's published, without having to visit the websites we have taken the feed from.
2. Feeds are generally known as RSS ('Really Simple Syndication') which are just web pages, designed to be read by computers rather than people.
3. New feed are standardized, machine readable collections of content, which can be processed further, to some extent the content of you site, without the encumbrance of the template and layout.