Signing for release build error

 Hello Corona users i am having some diffuculties signing my application so i can post it on google play. I have followed this guide ( http://docs.coronalabs.com/guide/distribution/androidBuild/index.html ) and yet i cant do it. I am having a problem with the command prompt it says “keytool is not a internal or external command” and idk what to do.

If someone could guide me or make a video it could help me and many other users that face the same problem.

Thank you