Hi Edward, you can call the SendEmail or SendEmailWithTemplate microflows from a microflow of your own from any of your own forms, provided you can pass suitable parameters (Email address, subject, message).
I noticed that when calling the sendEmail microflow directly, it slowed down record saves significantly while it waited for this process to complete, so I built a separate EmailQueue form and just created records in that form when I want to send an email. A scheduled event is then used to process the entries in the EmailQueue form to actually do the send in the background without slowing down the user interface. That seems to work quite well.
In the "Use me" folder you can find several microflows to send Emails. You can call the 'SendEmailMessage' microflow from your own custom save microflow to send an email.