Please, tell me on what site I should register my web page in order to obtain information about how many people visited my web, from what country they accessed my web page. The latter is necessary.

Thanks.

There are tons of sites that do just this.
Web Stats (http://www.google.co.uk/search?client=firefox-a&rls=org.mozilla%3Aen-US%3Aofficial_s&hl=en&q=web+stats&meta=&btnG=Google+Search).
I know it's a Google link, but as there are so many to choose from it's best to have a look for yourself and find one you like.

Please, tell me on what site I should register my web page in order to obtain information about how many people visited my web, from what country they accessed my web page. The latter is necessary.

Thanks.

There are loads of stats places as Ben mentioned, but the country aspect will not be accurate. The WEB server can only tell the IP of the visitior. They can guess the country based on the ISP that owns that IP. But that's only a guess.

Also, check your hosting company's control panel. You may have one of them already installed there.