How Can I Exclude Category From Showing Up on Homepage?

Hello

I'm trying to exclude one category & sub-categories from the homepage, I have found a code online to do it but where do I have to paste the code to?

Here is the code:

function exclude_category_home( $query ) {
if ( $query->is_home ) {
$query->set( 'cat', '-5' );
}
return $query;
}
 
add_filter( 'pre_get_posts', 'exclude_category_home' );