I hope this helps:
Basically create a directory, let's call it import/
Under this directory have 1 folder for each study so:
in each of those directories, have a study.xml file (often in ddi format, but in your case, I suspect dublin core) and any additional files associated with that study. You can also place these files in subdirectories, in which case the directory names will be used as the file category.
So for study1:
The above would convert to 1 study in the chosen dataverse, with 5 associated files; file1 would not have a category, while others would.
Does that help clarify things?