Click [Here](https://www.virtualbox.org/wiki/Downloads) to visit the VirtualBox website. You will see the following page. Click the "OS X host" and it will automatically download a dmg file, which includes the VirtualBox App.
Click the dmg file that was just downloaded, and a verify screen vill pop up. Double click the box icon with the name "VirtualBox.pkg". This will take you to the installation screen.
**Note**: It will notice you that your macOS didn't allow the unknown source. If you see the prompt box, press the setting button instead of the "OK" button. You can select the `allow` option in settings and restart the install.