Instructions
Scroll over to the "PlayStation Network" icon on your XMB dashboard, then select the "SignUp for PlayStation Network" option by pressing the "X" button.
Highlight the "Create a New Account" option, then press "X." This will bring up four prompt boxes that you need to fill out with your personal information, including your date of birth and email address. You must also agree to the End-User License Agreement.
Press "Continue" at the bottom of each prompt box to move on to the next one. Create a password for your PSN account. Select "Continue," then enter your PSN User Name -- this is the name that is displayed when you play online.
Read through the information displayed on the final screen to make sure that you have entered all of your information correctly. If you need to fix something, click the "Edit" button next to the field with the error. When all of the information is entered correctly, press the "Confirm" button to create your PSN account.