how do you stream amazon movie from PC to apple tv

Since Amazon has not developed a native app for the ATV you would need to AirPlay from another device...

http://www.appletvhacks.net/2014/04/09/how-to-stream-amazon-prime-instant-on-app le-tv/

with a mac you can use airplay mirror

Use AirPlay to display video from your Mac on an HDTV - Apple Support

with windows and older versions of OS X one needs to buy the program called airparrot