I have a task to accomplish don’t know where to start.need help

Scenario:
Step 1:: On a SalesOrder, Create 2 custom fields (Free form text) named “Popup Value 1” & and “Popup Value 2”. Show them in the primary information section (Main Tab) on the sales order.
I have done this .
Step 2:: When clicked on Save button after filling the required fields on the sales order, You need to capture the submit event on client side using client script and show a popup that will show 2 text fields for user to enter values in with the labels as the custom fields and a button. On click of the button the values of the popup should be set in the custom fields of the SalesOrder and then the original save function should resume after that.
I have to accomplish in SuiteScript 1.0