If your wordpress theme doesn't support 'Menu' you can try this post for 'Menu' support.

some low quality wordpress theme doesn't support menu. or when a wordpress theme maker create new custom theme then need menu support for themee. however if your wordpress theme doesn't support menu then pressspot can help you for doing this then copy this code:

function register_my_menus() {
  register_nav_menus(
    array( 'header-menu' => __( 'Header Menu' ) )
  );
}
add_action( 'init', 'register_my_menus' );

after copy paste in in your themes 'functions.php' file and save it. now you copy this code:

<?php wp_nav_menu( array( 'theme_location' => 'header-menu' ) ); ?>

after copy paste it where you can display your menu. you also done. for many tips and code visit pressspot blog more times. pressspot blog is an updated blog.
Thanks.