The Action Bar contains a Lock Button. Inside the lock you see the number for your current authorization level:
Click the Lock Button in the bottom bar (see Step 1) to bring up the Authorize dialog. Enter the password and click "Authorize".
The password will be used to verify you for the highest possible clearance. This means Organize will first try to check your entered password against Universal Access. If the password fits, you get Universal Access to all data. If not it will check the next lower clearance (Top Secret) to see if the password fits. This will be repeated through all security levels. If the password doesn't fit on any level, the clearance will be revoked to level 0 (Unclassified only).
This means if you set passwords for the different clearance levels and want to leave your device unattended just tap the Lock Button and press "Authorize" without entering a password. This will set Organize to clearance level 0 and show only unclassified information. As soon as you get back, tap the Lock Button again and enter your password to get a higher clearance. This will show the additional items with assigned security levels.