It is so easy and simple if you want to add password protection to your Mac’s screensaver.
First, open System Preferences. It could be in your Dock, or you can find it by clicking the apple in the upper left corner of your screen and select “System Preferences” from the list.
When System Preferences has appeared, click the “Security” icon.
After the “Security” preference pane appear. Now, pleasr check the box next to the text saying “Required password to wake this computer from sleep or screen saver”.
And now, your Mac’s screensaver is having a password!