When development mode is enabled in Salesforce we can observe two split screens in Visualforce page edit mode. Enabling development in salesforce we can develop Visualforce pages in view state. It is difficult for every new user to salesforce.com to build Visualforce pages without enabling development mode in salesforce.
1. Goto your name and Click on My Settings:
2. Expand Personal Information section --> Advanced User Details:
3. Click on Edit: