A schedule or multi-track CSV can fill several people lists on each session. Add one column per list, and put the list's name after a colon in the heading — for example People IDs: Speakers and People IDs: Moderators.
Each column fills the list with that name on every session, and creates the list if a session doesn't have it yet. New lists go below a session's existing lists; an import never reorders lists you've arranged in the editor.
Only a heading that says People IDs fills a people list. Capitals and spacing don't matter, so people ids and People_IDs work too. A heading with any other wording — Sponsor IDs: Hosts, say — isn't recognised: the column turns up in Map your Fields with no field chosen, and if you leave it that way it isn't imported.
Setting the list name during the import
In the import's Map your Fields step, every column mapped to People IDs has a List Name. A named column's box is filled in from the heading, and you can change it there instead of editing your file.
A plain People IDs column fills each session's first people list. Click Name this list… to send it to a named list instead.
If two columns point at the same list, the import stops and asks you to rename or remove one.
Lists of documents can't be imported from a CSV. Import your sessions first, then add documents in the editor.
Related articles that might be helpful:
Start with the guide to lists on schedule items
See how you can attach people to schedule items via the CSV import
See how you can add a people list in the editor
See what happens when you update people lists with a re-import