Hi @homax
On this page, you will find examples of sorting by a custom field:
http://www.advancedcustomfields.com/resources/getting-started/code-examples/
To orderby a custom field value, it is very simple but you will need to read up on it here:
http://codex.wordpress.org/Class_Reference/WP_Query#Order_.26_Orderby_Parameters
Also, these examples use the get_posts function, but you may need to use the pre_get_posts filter if you want to override the core query!
Cheers
E
