if i want to buy movies,how can i do it? i m not from u.s.

First, check this web page to see if Apple has been able to license movies for sale in your country:

http://support.apple.com/kb/TS3599

If they do offer movies in your country, then you buy them through iTunes or from an iOS device like you would any other content. If Apple does not offer movies in your country, then you will have to look to some other download store.

Regards.