How iMovie works (simple question)

Just want to confirm how I think iMovie works before deleting stuff. I copied a bunch of old (non-apple-device recorded) videos to my computer and then imported them to iMovie. That makes copies of the files, correct? So if I delete video clips from iMovie for the purpose of freeing up some HD space, I can always copy them again from the folder on my computer--or something like that, right? And, if I delete clips from iPhoto that are also in iMovie, I won't lose the file in iMovie, right?