There's been a bit of controversy recently regarding the security of passwords saved within Google Chrome. While Google's head of browser security says it isn't a big deal, some users aren't comfortable with the level of security automatically provided by Chrome. If you're one of those people, you're in luck. The good folks over at iMore have put together an overview of different ways OS X users can quickly secure their computer, even if they can't secure Chrome.
The first step is to go to your Security & Privacy settings, found in the System Preferences section of the Menu. Under the General tab click "Require password after sleep or screen saver begins."
This will require anyone who opens up your computer when you're not using it to, at bare minimum, personally know your password before they can access your content.
Once the setting is activated, you can instantly lock your Mac with the help of some simple keyboard shortcuts. This setting will depend on if you have an Eject button on your computer or not. If you have an Eject button simply press Control + Shift + Eject to lock your computer.
If you're using a model that doesn't have an eject button replace Eject with the Power button, or Control + Shift + Power.
You can also lock your Mac using Hot Corners. For that information, head over to iMore for their tutorial.