how i can this log in system with yahoo,twitter,facebook etc

Question

in many sites i can see

how i can do that is must tell every company or what?

Answer 1

It's OpenID. You can implement it in PHP easily by looking for PHP OpenID Libraries/Classes.

See http://openid.net/add-openid/add-getting-started/ to get started on developing authentication with OpenID.

Unfortunately, Facebook and Twitter has a complete different set of authorization api and thus you cannot use OpenID for Twitter and Facebook. Instead you can use their API.