create category upon saving post and save post in that category

The primary thing you’ll need to use here is the save_post hook in WordPress to execute your code right after a post is saved. Read up on the save_post hook on the WordPress codex first and then come back here.

The next part is assigning the post to a taxonomy term. This can be done easily with wp_set_post_terms() function.

You’ll end up with something basically like the below code that you can stick into your functions.php:

<?php
function save_suggestions_term( $post_id ) {
  // Check the post-type of the post being saved is our type
  $suggestions_post_type_slug = 'suggestion';
  if ( $suggestions_post_type_slug != $_POST['post_type'] ) {
    return; // Not ours - stop
  }

  // You'll need to figure out the name of your category.
  // You'll have $_REQUEST that you can get the fields that were just saved 
  $suggestion_term = 'Actors';

  $taxonomy = 'category'; // The name of the taxonomy the term belongs in
  wp_set_post_terms( $post_id, array($suggestion_term), $taxonomy );

}
add_action( 'save_post', 'save_suggestions_term' );

Note that wp_set_post_terms will create the term if it doesn’t already exists or add it to an existing one. This will run each time the post is saved again which means if you change the values of the input fields that are used in creating the taxonomy term name, the taxonomy term will change too.