Ok. The topic can be complicated but let me see if I can explain it. RSS is Really Simple Syndication. An RSS document (called "feed", "web feed", or "channel") includes the full or summarized text, and metadata, like publishing date and author's name of the contents of the website. RSS is a type of web feed which allows users and applications to access updates to websites in a standardized, computer-readable format.
You can subscribe to updates of a web site using software, an RSS reader, which can read the website RSS feed. If you subscribe to multiple websites you can use an RSS aggregator which is a web application which combines syndicated web content, aka RSS feeds, from multiple blogs, podcasts, and video blogs (vlogs) in one location for easy viewing. The RSS aggregator will automatically check the RSS feeds for new content.
FreshRSS is an RSS feed agregator.
More info here: