You should use pre_get_posts
to alter the main query on the home page.
With the proper conditional tags and parameters (check WP_Query
for available parameters) you can achieve what you need
You can do the following to just display posts from a given tag on your homepage
add_action( 'pre_get_posts', function ( $query ) {
if ( !is_admin() && $query->is_home() && $query->is_main_query() ) {
$query->set( 'tag', 'SLUG_OF_TAG' );
}
});