In IBM Integration Bus, you have several options on how to create an HTTP interface to external programs.
If you want to use a standard interface definition, there are specialised development artefacts which simplify that process. If you use WSDL for Web Service interactions then create an Integration Service, and if you use Swagger to define REST-style actions over a set of resources then create a REST API. In both of those cases, you can concentrate on implementing handlers for a particular request and the container handles the routing.
See the Integration Services or REST tutorials for those examples.
However there are some http integration requirements which don't fit either of these categories. This tutorial shows how to create a message flow which listens for any http request on a particular URL. The request is processed directly by the message flow and an http response is built. In this case, the processing is a transformation step using a Mapping node.
You will import the message flow to your Integration Toolkit workspace, and send an HTTP request to the message flow by using the Flow exerciser, and observe how that request is represented in a message flow.