you can just drag and drop. If that doesn't answer your question, we'd need a bit more context/a description of what you're trying and what's not working.
see my answer above. If you don't understand or it doesn't work, please ask more specific questions. (If it's easier for you, we do read most Western European languages, so you can write in any of those).
My guess: yashsoni06/wintermario have references with attachments in their personal libraries, and the attachments do not copy over when the reference is dragged to a group library.
I have files and I will sent to a group where I'm inscrit.