From PackRat Recipe Wiki

Your pack is where all of the cards you are currently collecting goes. A pack can only hold 15 cards (or 30 if you purchase an XL Subscription).

The top section is where your cards are located.

The bottom section shows your recent activity and comments. If you click "Smack Talk" next to the word "History," then it filters out all the recent activity to show just your Smack Talk wall.