[A] In order to add dispatch details open the invoice against which you want to send it and click on Other Action >> Dispatch.
[B] Now enter the details and click on the Dispatch.
[C] After clicking on Dispatch your customer will receive a mail of the details and it can be seen in the transaction timeline (Note - Customer will not receive the mail in case you don't have mail service ON for Invoices).
Keywords: Dispatch Detail, Fill Dispatch