The best practice is to create a proposal or estimate that transitions into a work order, which can then be converted into an invoice. However, there's also the option to create an invoice directly without following the full workflow. All that's needed is a customer account to attach the invoice to.
To create an invoice, first, you want to make sure you have an account (Customer) created to attach that invoice to. Once you have that created, next you'll
Go to the invoice section on the top of the screen.
Select "+ New Invoice" on the top right side of the screen.
Select what account (customer) this is for, then select "Without a Job"
Enter all the details on this page, just like you would for a regular proposal/work order. Then you can send it out to the customer or input payment information on your end.
Let us know if you have any questions!