Change most recent posts to a specific category

I apologize if I have missed anything but I was unable to find this covered. I have looked elsewhere to find the proper code to change in order to have the front page default to a specific category of posts, but I cannot seem to find it within the editor on this theme. I have also tried to wing using two different Custom CSS plugins to drop the following code in ( $query ) { if ( $query->is_home() && $query->is_main_query() ) { $query->set( ‘cat’, ‘11’); } } add_action( ‘pre_get_posts’, ‘my_home_category’ ); (stolen from another forum)

Can you direct me to how I might change this please?

I have also tried the following <?php
if ( is_home() ) {
query_posts( ‘cat=-1’ );

to exclude a category by adding it into the index.php and it does not work

I grant I am very long separated from doing any of this so please bear with me.

My site is