These are all customer orders created manually or from a quotation which can then be converted to a sales order or directly to a sales invoice.
When you've created your sales order you can click on Send this enables you to email the order to your customer or, you can register it as sent. Either way, by clicking on send the system retains a copy of the sales order within Current orders.
Once your customer has confirmed the order is good to go you can tick the box on the left hand side and click Transfer to invoicing if you need to amend the order, click on the edit icon far right, once inside the order click 'Cancel sent status' this allows you to edit the order, you can then click Send again, email back to the customer and when ready, transfer to invoicing.