Hi @mukul123 ,
Transactional messages are real time communications. Example, It could be a welcome message after creating an account, a confirmation that an order has shipped, an invoice, a message confirming a password change, a notification after a customer browsed your website, a product unavailability communication, an account statement, etc.
Refer this document - Transactional message for more details on how to implement and configure transaction message and about event type.