Matias Mann

I would advice to use a plugin such as Yoast.

If you want to do it manually.
1) In your theme functions add:

/**
 * Modify Meta Description on Single Posts
 */
function developress_meta_description() {
	global $post;
	// Get the description meta from a custom field
    if ( is_single() ) {
		$description_meta = get_post_meta($post->ID, 'description_meta', true);
        $description_meta = strip_tags( $description_meta);
        $description_meta = strip_shortcodes( $description_meta );
        $description_meta = str_replace( array("\n", "\r", "\t"), ' ', $description_meta );
        $description_meta = mb_substr( $description_meta, 0, 300, 'utf8' );
        echo '<meta name="description" content="' . $description_meta . '" />' . "\n";
    }
}
add_action( 'wp_head', 'developress_meta_description');

2) In each post you want to add a meta description. create a custom field named “description_meta”

This is for the meta description. For the title it can be done with a title filter.

1) Go to Settings > Permalinks.
2) Save the configuration to flush the permalinks.
Check if it works.

Have you updated wordpress recently?

Try activating the default theme.
If the menu appears in the location it is a theme related issue.