Open the course and tap "Download course" — every video and PDF in it is saved together, and plays with no network at all. You can remove the download any time to free the space.

The confirm sheet shows the exact size before the first byte moves, so you decide with the number in front of you. Removing a download frees that space immediately.

Downloads live on the device, not in your account — clearing app storage, reinstalling, or the phone reclaiming space can remove them. Your library itself is untouched: open the course and download it again.