Sales order is used to record a sale that you plan to fulfill in the future. It helps you keep track of items you promised to customers.
IMPORTANT: Sales order is only available in QuickBooks Desktop Premier and Enterprise.
Perform these steps to turn on Sales Order:

Sign in to the QuickBooks company file as Admin.
From the QuickBooks Edit menu, select Preferences.
On the left pane, choose Sales & Customers then go to the Company Preferences tab.
Put a check mark on the Enable Sales Order box then OK.

Workflow 1: Estimate - Sales Order - Invoice - Payment – Deposit.

Use this workflow if you need to send a proposal or quote to your customer that you will later turn to a sales order before you create an invoice and collect payments.
IMPORTANT: Sales Order is only available in QuickBooks Desktop Premier or Enterprise.

This workflow contains the following steps:

Workflow 2: Sales Order - Invoice - Payment Deposit.

Use this workflow if you are not required to send proposals or quotes to your customers but you still need to use sales order to manage the sale of your products and services.
This workflow contains the following steps:

Create a sales order from scratch.

Follow these steps if your business does not require sending estimates before creating sales orders.
From the QuickBooks Home screen or the Customers menu, go to Sales Orders/Create Sales Orders.

Or at the Home page, select the icon as shown below:

On main screen of Purchase Orders, select the icon as shown below:

Enter sale order header.

Picture: Header of sale order.

From the Customer: Job drop-down, select a customer or customer job. If the customer or job is not on the list yet, you can click Add New.

Fill in the relevant information at the top of the form like the Date and S.O. No.
Ship to: select a address as shown below:

Ship date.
Ship via: enter name to search and choose ship via from list.

Enter sale Item for SO.

In the detail area, select the item(s).
Note: When you select or add an item, the description and amount are automatically populated based on the description and unit cost entered when the item was set up. You can delete or modify this when creating Sales Orders.

Item: Good, Service. Enter item name to search and choose item from list.

Decription: description about item, note....
Ordered: quantity of item ordered.
U/M: Unit of Measure.
Amount: Total amount of item.

(Optional) If you want to apply a discount, you need to create a discount item.

From the QuickBooks Lists menu, select Item List.
Right click anywhere and click New.
In the New Item window, select the Type drop-down and choose Discount.
Enter an Item Name/Number and a brief Description.
In the Amount or % field, enter the discount amount or percentage. If your discount amounts vary, you may want to leave the Amount or % field blank and enter the amount directly on your sales forms.
From the Account drop-down, choose the income account you want to use to track discounts you give to customers.
Select an appropriate Tax Code for the item then OK.

After you have entered the full information of the SO, select icon as show below:

Create a sales order from an estimate.

Follow these steps if you have previously provided an estimate to your customers and you need to create a sales order for it.

Look for and open the correct estimate.
Select Create Sales Order at the top of the estimate form.

When the sales order appears, edit the information as needed.
Click Save & Close.

Save a SO as PDF file.

Click "Save" and choose "Save as PDF" as shown below:

Attach file into the SO.

Attach a new file.

Select icon as shown below:

On Attachment screen, drop document from Outlook, your desktop, or folders into area as shown below:

Also, you can attach files from the scanner, Doc Center.
Click "Done" to complete.