Then person visit canvas page of my app i must know install he my app on his profile. or just click on another person.?
and why "hello world" example works only when people who view my page have this app too. If he just view it and haven't install it isn't working.

beforehand thanks

Try this to determine if the current user (viewer) has the app installed:

gadgets.views.getParams().installState

A value of "0" means uninstalled, "1" means installed, and "2" means they're a new install.

Chad