you mean i must put my webpage on arduino to be the server so when i use get function it deals with it right ?
When your browser generates the GET request, yes.
is it possible to make a webpage on arduino with login (username and password) on it ? even for one user !
Yes, but...
In general a script on the client deals with the submitted data before the GET command gets sent to the server. The client side script encrypts the password. The server then tests the encrypted password against the stored encrypted password. While the Arduino is capable of comparing encrypted arrays of bytes, it generally can't serve up pages that contain client-side code. So, you'll have to send text (password) in clear to the Arduino. Which pretty much negates the security aspect of a login system.