New To FeedBurner, How Does It Work?

Ok Well im starting a new blog, resource site and i know feedburner is a great way to attract readers so I signed up put the code up and all but I dont understand how it all works.

1. How are the number of readers determined?

2. Do people have to subscribe with an aggregator?

Those are just a few, a general explanation would be great, Also everyone check out www.JuicyCode.com its gonna be cool.