My example 5,470,270 is a utility patent, which the majority of patents are. Utility patents need no special letters. If you are searching for a different kind of patent like a design patent, then you will need both a letter and a number. For example, design patent numbered 265,332 would be written D265,332 in the query box.
The Patent Number Search Page has examples of all the letters representing different kinds of patents. Don't worry about that right now. While you are learning we will be sticking with utility and design patents.
Note: The circle around the search button was added as instructions. The real search page will not have any such helpers.