Most bloggers offer RSS feeds of their blogs. Many other content-producing Web sites, such as radio stations, magazines, newspapers, etc. offer RSS feeds for their content as well.
An RSS feed allows you, as a reader, to subscribe to receive notification whenever your favorite site is updated. You can receive these feeds via email, or you can sign up at Bloglines and configure yourself a Web page to aggregate all your daily reads.
Bloglines is for both bloggers and readers. (All bloggers are readers, but all readers are not necessarily bloggers.) Bloglines also allows you to keep track of how many readers have subscribed to your blog.
Don't know what to subscribe to? Here's a suggestion, for starters: Simon Dumenco, a.k.a. "The Media Guy," writes a weekly column on AdAge.com. Find his colum, find his RSS feed, and subscribe to him.