Sales Freight charges booking

Hello Experts,

We started the new plant & production as well.

Last month we done our first month sale in FOB and CIF term. Usually we are booking in the freight charges in FB60 with sales cost center.

What is the purpose of sales order number using while booking vendor invoice for freight charges in FB60.

If we input the sales order in FB60 (Freight charges booking) what kind of report we can generate in SAP.

Regards,

Riyaz