Q: How do I copy a DVD using my iMac?

Is this a personal DVD or a commercial movie? If it's a personal DVD simply right click it in Finder and select Burn and follow the on-screen prompts.

These are old instructions, but they may still work - you need to create a disk image of the contents to copy/burn to the blank DVD. You should be able to use Disk Utility for that. Once you have Disk Utility open, click on Help and you'll find a "duplicate a disk' section with instructions.

I always use Roxio Toast for this as that process does things automatically.

Edit: it would not allow me to link to the old Apple article - the spam filters must have been changed.

I see, if it's a CamCorder recording then I would recommend following the directions given or using iMovie to import the movie and then use iMovie to help you export it to a DVD. If you have never done this please click:

https://www.apple.com/support/mac-apps/imovie/

Since it's already on a DVD, iMovie can't import it without converting it first.

FWIW, I am not able to post what I had intended as the spam filters are going wild and I have no clue what/which word(s) are being caught. It will have to wait until I hear back (posted in FHB).

Found that I should be able to post a screenshot of my intended post (and it is the spam filters at work) - so here is what I was going to say:

Please see Disk Utility 12.x: Duplicate a disk, CD, or DVD.