RSS is generally used to notify others of the latest news and updates to a site. Confluence reads incoming RSS and creates outgoing RSS. It allows you to stay informed of the latest current affairs of others and allows you to tell them of your own.
Displaying RSS from other sites
If another site publishes an RSS feed, you can include its contents in a Confluence page by including the 'RSS' macro in the page.
E.g. Here is the macro code for displaying an RSS feed published by the BBC: