Can anyone tell me what is RSS and how it work with websites or blogs?

Online publishers syndicate their content using a specific format so people can subscribe to these feeds and receive the content without having to regularly visit your site to find out if you have any new content.

People will use a feed reader or news aggregator software to grab the RSS feeds from various sites and display them in a the app in a consolidated manner.

RSS is basically Really Simple Syndication (RSS) that is an XML-based document format for the syndication of web content so that it can be republished on other sites or downloaded periodically and presented to users. The RSS 2.0 specification describes how to create RSS documents.
An RSS document, also called a feed, MUST conform to the XML 1.0 specification and MAY contain elements and attributes defined in a namespace according to the Namespaces in XML specification.
A sample feed demonstrates all of the elements available in RSS. A namespace sample shows the same feed extended by the Creative Commons and TrackBack namespaces.