FeedBurner is a third-party application that is owned by Google, which means you need a Google Account to use their free service. To signup just go to FeedBurner.com and register. To get started, enter your Web Site's URL into the "Burn a Feed right this instant" box on their homepage and press "next". During the setup you will choose a name for your RSS feed, and a URL string (i.e. http://feeds2.feedburner.com/yoursitename). You can also choose from a number of tracking options during setup as well.
Once you have your FeedBurner URL, you just need to enter it into your CP5 Site. Log into the administration area for your Site and navigate to Start Page> Header And Footer. Create an HTML element under the "Top Bar" section in the upper left corner. Paste in the following code, and modify the areas that say "YourSite" to match your FeedBurner URL and your RSS Title:
<link rel="alternate" href="http://feeds2.feedburner.com/YourSite?format=xml" type="application/rss+xml" title="Your Site RSS" />
Now you want to create a link to the FeedBurner RSS feed so your users can easily subscribe to it. To create a link in your Site's navigation go to the "SubPages" tab and press "Create new link". Label the link "RSS" or "Subscribe" and paste in your FeedBurner URL. You're all set to start tracking your RSS subscribers!
Please Note: Inserting the FeedBurner code into your Site does not overwrite your CP5 RSS feed, it creates an additional one. It is best practice to create an RSS/Subscribe link from your navigation, footer area or in the right column of your Site so that users can easily add it to their RSS reader.