RSS stands for Rich Site Summary, and is a method by which one can subscribe to frequently updated information online, much like how one might receive the text of a blog post in an email that is automatically sent when the blog is updated. There is an widget in Wordpress which allows people to easily subscribe to the content of your site through RSS.
Go to Appearance > Widgets.
To add an RSS widget, such as NAMI News, drag the RSS to a location. In the popup form, enter the RSS feed URL, add a Title, and other options. Click Save.