Based on what you wrote in your post, the process to copy DVD to DVD is a 'copy and paste' sort of thing.
Since Macs (or nearly all computers) only have 1 DVD writer, you have to copy the DVD completely to your hard drive, then burn that data to a disk. Toast clearly has the ability to burn DVDs, but you might need another application to copy the original disk, though check Toast first. If it is a movie dvd that you own, you'll need a program like MactheRipper. Just make sure you're not doing anything in a legal gray area.