We secure your locked workstation with master password. You choose it and it is good for all administration tasks in the locked workstation. You will also need it for unlocking your workstation. In addition to that, a lot of times you want to delegate ability to reboot your workstation to somebody else. Choose a separate password for doing that and give it to somebody else. This person will only be able to reboot and shut down this machine, but not change any settings.
Please remember your master password. Do not rush your configuration into a locked mode. This software is designed to not let anybody who does not know the master password to control any aspect of the workstation. If you forget your master password, you will not be able to do anything with this PC and will have to reinstall your OS