Click the download link from your browser. Safari typically saves these to the Downloads folder, which you can access via the Dock or Finder.
If the app won't open, go to System Settings > Privacy & Security and click "Open Anyway". Download MAC dmg
A window will appear. Often, you simply drag the application icon into the Applications folder shortcut within that window. Click the download link from your browser
Double-click the downloaded .dmg file to "mount" it. It will act like a virtual drive on your desktop or in your Finder sidebar. Download MAC dmg