When you are making your first steps with the application, you will have access to some examples. These examples are ideal to be able to setup a first channel in a few seconds, and being able to test the application.
The application can also make suggestions based on the other elements present in your channel.
In the following example, a gateway IN of type MessageRecord has already been set to the current channel. The application will automatically suggest only one MessageDefinition to use, because it knows the format of files generated by this gateway.