I'm trying to get attachments to save to a document library, and I found a good article here to follow. But the instructor uses Dictionary variable types, and on premise versions of Nintex seem to not have this variable.
Can I use Collection variable types in place of dictionary, and is there a good example of how to convert dictionary to colleciton?
yes, you should be able to use collections in place of dictionaries.
these series of articles from Vadim Tabakman might help you