How to Link to WP Pages Internally and Extenally

by

Use this to output correct link:

<?php 
   $page = get_page_by_title( 'Store' );
   echo get_permalink( $page );
?>

Or if you know ID of your page (you can get ID from administration), you can use just (if ID is 2)

<?php echo get_permalink( 2 ); ?>

You can read more about get_permalink function here

And I would also suggest you to read something about wp_nav_menu function to enable your theme to use Navigation menus.