Once you've created a workflow, you can add automation by attaching email templates to steps in the workflow.
Attaching Email/SMS Templates To Workflows
Go to one of the email or SMS steps in a given workflow and click on the paper clip icon to the right of the description.
Select the template you want to attach by clicking on it.
Select whether or not to send out the email/SMS template automatically when the workflow task becomes due by clicking the lightning icon (it will be colored blue if automatic, grey if manual; the step icon will also have a blue background color). If selected, the workflow step will automatically be completed once the email or text message is sent out.
The email will be sent out on behalf of the agent assigned to the lead when the workflow task comes due. Alternatively, you could assign it to a single user all the time even if the user isn't assigned to the lead. Read this article for more details. The assigned agent's email signature will automatically be appended to the end of the email template.
If an email workflow task that is set to auto-send is manually completed prior to the due date, the email will NOT be automatically sent out.
If a workflow step has an email attached to it, but the auto-send option is turned off, the workflow step will create a task that has the email template attached for convenient reference when manually sending out an email.
If you want to edit the email template from the workflow page itself, simply click on the template chip, make any edits you want and click "Save".