The main window contains three basic steps (starting from the top):
Source files definition (Path, Filter and Prefix).
Loops and metadata definition.
File/Frame order definition (list of individual files/frames with associated position in the experiment).
At the bottom of the window, the status of the definition is displayed. It is not possible to proceed until all the necessary information is provided.
Typically, the user starts by defining the source files and then adds the loops and assigns indexes until all files/frames are assigned an unambiguous position in the experiment.