RSS is an acronym for Really Simple Syndication. It brings new content to you instead of you having to go to it. It is a way for web sites to send brief descriptions of new or changed content on their web site along with a link to the full story or referenced page.
RSS is a very useful way of quickly getting content you care about. Many information junkies, me included, used to have countless favorites or bookmarks in their browsers to stay abreast of news, hobbies, work related items, and so forth. At one time I even went to the trouble of making a sub-domain with some of my often-visited sites. Using RSS feeds made that site obsolete, and it has been deleted.
As mentioned earlier and worth repeating, once sites with RSS feeds are configured into a browser such as Firefox’s live bookmarks, into Outlook, or with a standalone program such as RSS Bandit you no longer must go to the sites to find new information, the new information comes to you. Programs or plug-ins that collect the RSS feeds are often called aggregators or readers.
In December, 2005, Microsoft and a host of others reached a consensus that this icon 
will be used to indicate a site with RSS feeds. Standardizing on the same icon reduced confusion, for a time, because now few sites with RSS display this icon. But don’t be too concerned because modern browsers and standalone RSS aggregator apps have methods to detect the XML code that makes RSS work. Refer to your browser’s or app’s help file how to populate RSS feeds from your favorite sites.
Your choice of an aggregator will depend on personal choice. Personal choices depend on layout and display preferences, if you want a plug-in for an existing program such as your preferred browser or e-mail program, or a standalone program. One desired feature is the ability to synchronize feeds you’ve read on multiple computers, tablets, and smart phones.
Further reading and useful links:
https://en.wikipedia.org/wiki/RSS Wikipedia article about RSS
https://www.wired.com/story/best-rss-feed-readers/ Nice Wired Magazine review of RSS Readers
http://www.feedly.com Nice integration into Chrome, my current go-to
http://www.rssbandit.org RSS Bandit’s home page, a standalone application