While browsing the Item, Customer, or Vendor Lists, you'll probably notice an icon on each line that looks like this:
This is the Info button. Double-clicking the button will take you to a special Info screen where you can view all sorts of information about the record in question. For example, when you click a particular Customer's Info button, you'll be taken to the Customer Info dialog where you can essentially view that Customer's entire transaction history.
Information about each of the Info screens can be found here: