What does the “Order” field do?

The Order option is useful if you have 2 or more widget areas that replace/merge the same widget area on overlapping conditions. In that case you can control the positioning of their widgets.

You can read more about that behavior here: https://dev.institute/docs/content-aware-sidebars/faq/what-is-the-difference-between-actions-replace-and-forced-replace/

I hope this helps!