Update Existing Record using SuiteScript

OK - first a confession - I have no idea what I'm doing with SuiteScript !

I'm looking at SuiteAnswer ID 74546 which shows how you can use SuiteScript and Workflow to update an existing Contact Record from a Lead Record.

I want to update a Sales Order Record from details in the Fulfilment Record - so I'm trying to adapt this to work for me.

I'm sure there are multiple things wrong with what I'm trying to do, but this is what I've done:

1. I've updated the script file and uploaded it:

function setSalesOrder() {

var salesorder_id = nlapiGetContext().getSetting('SCRIPT','custscript_salesorder_id');