This code is used to authenticate a user into a WordPress site. It takes in an array of credentials, which includes a username and password, as well as a boolean to remember the user login. The credentials are then passed to the wp_signon() function to authenticate the user. If the authentication is successful, the wp_set_current_user() function is used to set the authenticated user. In the case of an error, the get_error_message() function is used to get the error message.