Create the unique name for the new Event Type in the MAPT portal. Then you can access the drag-and-drop builder, where all your microservices (and a few extra MAPT microservices) will be available to create your event flow.
Select any microservices and drag a line from any of its Output Types to the next microservice that should be invoked.
Once saved, the event flow is live immediately, and any occurrence of that Event Type will be handled as you specified.