Is there a quick way to lock my Mac?
On macOS High Sierra, there is a standard key sequence and Apple menu item to lock your screen. 


Control-Command-Q or ^+⌘+Q






For older OS, ⇧+⌃+⏏ puts the display (only the display, not the whole computer) to sleep and will then prompt you for a password if you have enabled Require password [amount of time] after sleep or screen saver begins under System Preferences &gt; Security.

If your Mac does not have an &#x23CF; (eject) key, you can use ⇧+⌃+⌽ (power).