There might be several reasons when you will need to create a draft order.
1. You received an order and it did not show up in Oberlo because the product is not synced with Oberlo. You will need to override the product and create a draft order to be able to purchase the product from the supplier.
2. You received an order, but you cannot place it in Oberlo because the item weight does not meet the shipping method rules. You will need to create draft orders to split products into different orders.
Creating a Draft Order
To create a draft order, go to Shopify admin > Orders page and click on the “Create order” button.
From the newly opened page, add the product(s) your customer has ordered.
Then, add your customer shipping information.
Discount the order by 100% and click "Apply".
Finally, mark the order as paid and it will appear in Oberlo.
Go to the Orders page in Oberlo, and click on the blue “Order” button to purchase product(s) from the supplier.
To learn more about the order fulfillment, visit the Fulfilling Shopify orders in Oberlo article.