You tell Aperture which feeds you want to follow, and it works behind the scenes collecting new posts. Aperture can follow Microformats, JSON Feed, Atom and RSS feeds.
Aperture doesn't have its own interface for actually reading the posts it collects. Instead, it makes the data available via an API, and you can use a variety of apps to read your feeds!
Aperture provides a way to manage subscriptions and show some debugging info, but normally you won't interact with it after you've set it up, you'll use a reader.