Q: How do I burn copies of a DVD on my iMac

I want to make copies of a DVD (VHS home movies I converted to a DVD+RW disc) on my iMac. Tried downloading the DVD onto the hard drive thinking I should be able to then eject the original DVD, insert a blank DVD, open the file and then simply burn a copy onto the new, blank DVD disc. Not having any luck whatsoever.

Please help!

Thanks.