What is your question, @Paylos_paylos24? Telling other forum members that something is not a help does not get you more information. What part of the Guide do you not understand? Also, do you understand that purchase invoices are the method for recording incoming sales invoices from suppliers? Purchase invoices and sales invoices are financially unrelated.
Is it possible you mean that you have received three purchase orders from customers? If desired, you can enter those as sales orders in Manager, but sales orders have no financial impact. They are optional.