How do I set up my macbook to ask for a password everytime i

Go to System Preferences > Security

Check the box that says Require password after sleep or screen saver begins. When you close your laptop it is actually going to sleep, so when you open it again it'll ask for the password. Same for if you leave it open and the screen saver starts. ybarra-cgm.com

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Also disable automatic login, which will keep someone from just rebooting your computer and having it login automatically. ybarra-cgm.com

ybarra-cgm.com

Also go to System Preferences > Accounts and then click on Login Options in the bottom left. Choose the option at the top that says Display Login Windows as Name and Password. This way if they do reboot the computer they won't see a list of users, they'll have to know the username and password. If they have a list of users they only have to guess the password. Also uncheck the show restart sleep and shut down buttons, that'll keep them from easily resetting the computer with a button press. (Of course they could still just hold down the power button, but it is a good idea anyway)