Click on the download link, which will prompt this pop-up window. Choose "Save File."
Click orca_mac.zip and "Save file."
Once downloaded, the zip file will appear in your downloads. On Firefox and Safari, you can access the downloads in the browser toolbar. Double click on "orca_mac.zip."
Once your computer has extracted the ORCA file from the zip file, a window will appear with "ORCA.pkg."
Double click on ORCA.pkg. You might see this message:
Go to the apple in upper left-hand corner, and choose System Preferences.
Find the "Security and Privacy" option, and select "Open Anyway" where it mentions ORCA.
ORCA should then install. Follow the prompts to complete the installation.