From the Members -> Member List page. Click a member's £ button to access their already generated invoices.
The member's Invoices page has several features covered in the Viewing a member's invoices article.
The Send email button immediately triggers the system to send an email to the member if the system holds an email address for the member.
When the email is sent, the page reloads, and the Send email button changes to a Resend email button, and text is displayed to indicate an email has already been sent.
The member then receives the PDF invoice attached to an email message:
The content of the email message can be edited, see Editing the email invoice template.