MacBook Users

How Do I Allow Third Party Apps on Mac?
Select “Security & Privacy” from the “System Preferences” window. Select the “General” tab, and select the lock in the lower left corner to allow changes. Enter your computer username and password, then select “Unlock.” In the “Allow apps downloaded from:” section, select the radio button to the left of “Anywhere.”
How to Use Gatekeeper:
http://www.imore.com/how-use-gatekeeper-your-mac