I am the begineer in WP trying to convert my HTML site to Wordpress theme. Everything working fine but i want to link one page having name contact-us.php in my theme root directory , i want to link this page with contact us menu in the header.
The way you are doing things is not recommended. When you want to create a contact-us page create a template in Wordpress Page Templates
In the backoffice you can create a new page and select this template in the sidebar on the right
First you have to make a template to your contact us file. Use this code on the top of contact us file.
<?php
/**
* Template Name: Contact Us Page
*/
?>
And make a page from its backend and select contact us page template from the rightside. After that create a menu from menu section. I hope it will be work.