Command

The file to execute.

Parameters

This setting specifies the parameters to execute the file.

Show

The window state at startup.

Timing

Specifies when the selected command should be executed.
For launching files from setup package Before Installation, you need first add them on the "Additioanl Files" page using for the "Destination" field a variable: <SetupTempDir>

Wait Until Process Finishes

The installation waits for the given file to terminate before continuing.

Example: how to create a new folder
Command: <SystemDir>\cmd.exe
Parameters: /C mkdir "C:\New Folder"