To add feeds, you can:
1) Browse to the page you want updates from, then click on the green "Add Feeds" button at the bottom of the App Edge, and then select "Add *" at the top. The green indicates that there's a feed you can add.
OR
2) To manually add feeds, copy the RSS URL and then, click on the "App Center" button at the top of your App Edge, type in the URL of the sites you like in the box in the top right, and add the sites that appear.