A feed lets you read stuff from other sites on your reading page. If it's an LJ/IJ, you can just put in the URL and Dreamwidth will create a feed and add it to your page. On other blogs, look for a button that mentions RSS or feeds, and put that URL in.

My reading page - http://sonjadenise.dreamwidth.org/read
Shakesville (one of the feeds) - http://shakespearessister.blogspot.com

Basically, fewer clicks XD