To view the movie you'll need the latest version of QuickTime or Real Player

With QuickTime, Save the file to disk and open by clicking on "File - Open Movie in New Player" and browse to where you saved the file. Then click the play button on the bottom.

With Real Player, Open the file instead and run with Real Player. You might have to force Real Player to open the file if you've never run an *.mp4 file before.