If you want to be able to cut shapes or letters, besides what is on your Cricut cartridges, you also need to have one of the programs to do that. The two I know of are Sure Cuts a Lot and Make the Cut.
This video will help you prevent getting bad cuts with your Silhouette Cameo or Silhouette Cutting machines. Please come visit my blog to learn more about the things you can do with your Silhouette cutting machines and download some free cutting files and hopefully find some inspiration. http://www.paperpulse.blogspot.com/