Account module: To Bill

Hello;
ERPnext Version is: v7.2.14
What is the benefit of the “To Bill” in the account module? How I can use it?

Regards
Bilal

Can you please explain the context ?

“To Bill” is a label used to identify that your Sales Order is yet to be bill

I am talking about the below section, hopefully if someone can advise me how to use it?
Because, I created sales order and purchase received, and I did not see them in this section (To Bill), although I did not create for them invoices, so it should appear in To Bill if it is related to it (to bill sales or purchase order that has not generate for it an invoice), any advise?

Regards
Bilal