dont understand where this action takes in form action

hey there,

i am new to wordpress and trying to modify theme. but i am not able to track form action.

<form action="<?php echo appthemes_get_registration_url( 'login_post' ); ?>" method="post" class="login-form register-form custom" name="registerform" id="login-form">

where these action takes ? how data is stored ?
this is the function.php where i get above function.

function appthemes_get_registration_url( $context = 'display' ) {
	if ( current_theme_supports( 'app-login' ) && ( $page_id = APP_Registration::get_id() ) ) {
		$url = get_permalink( $page_id );
	} else {
		$url = site_url( 'wp-login.php?action=register' );
	}

	if ( ! empty( $_REQUEST['redirect_to'] ) ) {
		$url = add_query_arg( 'redirect_to', urlencode( $_REQUEST['redirect_to'] ), $url );
	}

	return esc_url( $url, null, $context );
}

can anyone help me with this issue?
i am stuck here.