For downloaded video: Click on the video you want. Follow the instructions for downloading the file to your computer. Once the file has finished downloading, open VLC. Using the VLC menu, click on "Open File". Browse to the file you have just downloaded. Select and open the file. Your video will begin playing automatically.
For streaming video: Click on the video you want to view. A pop-up box will appear asking which software you want to use to open the file. Browse your Mac for VLC. Click on VLC, click OK and your video will start playing automatically.