It's a CSV file to import into your software. This is the ONLY way to bulk import into the software and the file has to be done correctly or it won’t work. You answered questions about other CSV related things like custom fields for their CSV file. You have a formula for merging the categories posted on this page of your documentation:
From your documentation:
Category - specify the category your product belongs to. If the product should be imported into subcategory use pipe character "|" to separate parent and sub category, for example: "Computers|Keyboards", the product will be assigned to Keyboards category. In case you have categories in separate column, please merge them in Excel using the following formula:
| - is category delimiter
B2 - is your parent category column in .csv file and
C2 - is sub category column in .csv file.
If you need to assign the same product to multiple categories, use double delimiter, like this one: "Computers|Keyboards||Computers|Other" in your .csv file. In this case, product will be assigned both to Keyboards sub category and to Other subcategory while import. In our case Pipe is used as category delimiter.
Unfortunately your documentation is lacking but someone must know how to do it.