By default, WordPress allows you to add Tags to Posts, but not Pages.
After adding this code snippet to your website, you’ll be able to add a Tag to Pages and a Tags column will be added to the Pages table (/wp-admin/edit.php?post_type=page).
PHP
function my_allow_page_tags()
{
register_taxonomy_for_object_type("post_tag", "page");
}
add_action("init", "my_allow_page_tags");