To enable a PIN password, type pin at the Windows 8 Start Screen and then click on the Settings category.
When the search results appear, click on the Create or change PIN option to open the User Settings screen.
On the above screen click on the Create a PIN button. You will now be shown a screen asking you to confirm the password for the current account that you are configuring to use a PIN.
Enter the password for the currently logged in account and then press the OK button. You will now be shown a screen where you will need to create the PIN that you would like to use to login to your account.
When you next login to your account you will now be presented with a prompt to enter your PIN.