Could someone thoroughly explain to me what "RSS Feeds and Syndicates" real is and how it works . I seem not to understand them. I am not sure whether to involve them in my joomla site or not.

RSS feeds and Syndicates is a way to share information in a format which is common to all. RSS feed is nothing but a output of your latest content in a format which can be read by RSS reader.

If your site has RSS feed then anyone can get to know about latest content of your site just seeing your RSS feed. You can see eTI's latest posts by its RSS feed even without visiting eTI and if you like to read them full you can then come to that post from that RSS feed.