After your have downloaded the instagram-live-streamer-x.x.x.dmg file double click to open it
Drag the "instagram-live-streamer.app" into the "Applications" folder
After it finishes copying, open the "Applications" folder and find the "instagram-live-streamer" app.
"Right-Click" the app icon and select "Open"
A pop would show up saying its not signed. You can ignore the message for now and click on "Open"