To install Horos:
- Double-click the "Horos4.0.0RC5.dmg" file to open it
- Read and agree to the license
- The Horos disk image window open
- Drag the Horos.app icon from the disk image window to your Applications folder (not the App Store app). The disk image window contains an Applications folder link to the right side of the Horos.app icon. You can drag and drop the Horos.app onto this icon to install it.
I hope this helps.