Sales Order --> Bill

I need to run a nightly routine to bill a few sales orders that meet specific search criteria. The search is not a problem but I'm not familiar with how to manipulate a sales order.

Basically, I need to approve a sales order, then fulfill it, then bill it. I don't need to change any of the details of the order, just walk it through the steps. Is this just a matter of updating flags or are there specific functions for manipulating sales orders?

Thanks,
Walter Gibraltar.