This very much depends on what you want to achieve and using what systems/apps to achieve it. What Messaging technology do you want to use and interface with - the answer to that will give you many different answers to your question.
For example, if you want to send messages via Teams or WhatsApp or Slack - what APIs do these messaging tools have. Have you looked on the BP Digital Exchanges to see if the API interfaces already exist there (I know off the top of my head there is a Slack web service one). If you want to send SMS text messages you will probably need to purchase a service that sends text messages - how you interface with that service will again depend upon what APIs they have or how the UI of their service works.
The basis of your Blue Prism solution to call such an API or messaging service will be the same as any other Blue Prism solution you will have been taught how to build by following the training courses. Requests for the message to send would need to go into a BP work queue from whatever source the message requests will come from, your process logic will then call the objects that interface with the messaging app or service.
