When you first run it you will get news from both the Senate and House, but then you can drill down by state and to a particular member of Congress. You can find new proposed legislation, or track the status of any bill. You can see the latest votes from your legislator, and what bills they are sponsoring.
I gave the app a try and found it easy to use. I liked the idea of getting a map to my congressman's office, but it is only the DC office, not the local offices. Same for phone numbers. I consider these omissions surprising in an otherwise complete app. Also, when getting a map or digging deeper into a bill, I'm thrown out of the app to Apple Maps or Safari. It would be better to build the browser in, rather than forcing me to go back to the app. Other weaknesses look like they will get fixed in a future update, like push notifications for votes, committee listings and updates from the floor.
A similar free app that is universal is U.S. Congress Watch. I found the Congress app to have a nicer GUI and it was easier to use.
Congress is a worthwhile app for those interested in politics and tracking your local legislators. Congress requires iOS 6 or later and is optimized for the iPhone 5. It is not a universal app so it will need to be scaled up to fit the iPad screens.