Requirements: Mac OS X 10.8 (Mountain Lion) or newer
The Brick Viewer can be installed from a .dmg file.
First, download the Brick Viewer .dmg form here. Click on the downloaded file, this should open the image:
To install the Brick Viewer drag and drop the file to your applications folder
After this you have finished the installation process. You might need to restart your machine after this, otherwise the icons don't show up for some unknown reason.