There are several ways to use password protection for your Mac in the office: one way is to require your password on login, and the other way is to require your password during the day when it’s running, such as after the screensaver has come on.
To set a login password, go to your Systems Preferences and then click the Security icon in the top row. In that panel, tick the “Disable automatic login” box for all users in your Mac (even if you’re the only one). If the whole panel is grayed out, click the lock in the bottom left hand corner and enter your administrator password; then, the panel will be unlocked and you can make changes.
This will enable a password login, and the next time you start or restart your Mac to login, you’ll see your login name and icon with a box to enter your password. This password is the same as your administrator password.
The other way to password protect your Mac is to require a password during the day to get out of the screensaver or sleep mode. In the same Security Panel, the top tickbox enables your screensaver and/or sleep password, and so when the Mac wakes up or you tap the keyboard or mouse to bring it out of the screensaver, you will need to type in your administrator password.
And in order to enable the screensaver and password when you need to walk away from your desk without having to wait for the screensaver to come on, you can trigger the screensaver – and the password protection – any time you want by setting “hot corners” for the screensaver. A hot corner is a corner of the screen that reacts when you move the mouse to that corner, and is this case, you can set a corner to turn the screensaver on when you move the mouse to that corner.
Go to the Desktop and Screensaver panel in Systems Preferences and select Hot Corners in the bottom left hand corner. You’ll see dropdown menus for each of the four corners of your screen, and you can select which corner you want to activate the screensaver or display sleep. You can even set a hot corner to deactivate the screensaver, so it doesn’t come on at all.
These two passwords are not very secure and are only intended for casual security from people just snooping around. Someone can still boot from a DVD and disable them.
But if you want to set a more secure password for startup, you need to set a firmware password by using a utility on your OS X DVD. That means the password is set in the firmware of the computer and is more difficult to bypass. See Setting up firmware password protection in Mac OS X.
Setting a firmware password doesn’t change a screensaver or login or administrator password, if you set one of those as well. But once again, a firmware password is more secure that the login password, but it’s not perfect. The only perfect way to keep someone from starting up your Mac with a DVD is to lock the office not let anyone have physical access to your Mac.