Now that you understand the basic architecture of Visualforce, you can jump right into creating Visualforce pages. This section covers creating and modifying pages, and displaying related records.
Visualforce includes a new development method that allows you to immediately see the implementation of your Visualforce pages. This method, referred to as developer mode, is not turned on for all developers by default. To take advantage of this mode, check to make sure that your user profile includes this permission.
Go to Setup Manage Users Users and select your user. Click Edit and make sure ...