Custom Order Fields is an Add-On. If you don't see them when viewing a order you can install the Add-on.
Each order has four custom fields that appear at the bottom of orders in the control panel:
You can change the settings on those custom fields by going to Admin > Customisable Fields > Order Fields and select the field you would like to edit.
To display those fields on the Checkout page requires a change to the design template. Contact your web designer or our design team to make the changes.