The main run/debug configuration tab sets the project and
the name of the file to use for the launch. An example
is shown below.
If the file is a .nb file, then the launch will be a notebook file launch, as described in the section on launching notebooks.
If the file is a .mt file, then the launch will be a tester launch, as described in the section on unit testing.
You can also add information to create a Java launch to take place when Mathematica is launched. This is useful for debugging J/Link applications, and is described in more detail in the section on J/Link launches.