Two triggers: registration and subscription
Choose customer registration or completion of the subscription field as the automatic coupon condition. Registration creates a customer account; subscription is a signup through the subscription field. Select the rule for the action you want to encourage.
The coupon arrives by email
When the selected condition is met, a coupon is assigned to the customer and the code is sent by email. The rule handles delivery instead of requiring you to send each code manually. The customer can then use the received code.
Example: a welcome offer
Use the registration rule for an offer aimed at new account holders. Use the subscription rule to encourage subscription signups. Explain which action triggers the coupon and its usage conditions so the advertised offer matches the email.