How to Copy User defined columns from one workbook to another

Sorry. What I would like is for the macro to ask the user which columns they would like to be copied (this can be done as a loop if that's easier) and then for those columns to be pasted into the master (and the active cell will always be D1 for each sheet). Source workbook is already open.
I just re-worded what I had previously posted. So if this doesn't clarify let me know. I also bold-ed the original wording for my problem in the original post.