You can't format DVD-R disc because they are already formatted for burning and burning ONCE only. (ie put it straight into your DVD burning device and use the software that came with the device (ie Nero) to burn files. You can use the DVD-R (or any other discs if your device is compatible for burning; just be sure that if you're burning it for someone else, make sure their DVD device is compatible for the disc otherwise you have wasted a disc) to store files of any kind whether data, music etc, just select what you what to burn at the open window of the burning application (ie to burn files only; Nero, make a data DVD/CD etc).
If you're talking about eracing files etc. from a DVD-RW then it's a diff. story. Just use the DVD burning application (ie Nero Express; open app. click at open window the word 'MORE' then click erase disc). There are two type of for erasing quick and full. The full will take longer (30mins and up) but cleaner or otherwise use the quick (it just write a block in the sectors and when come to burning new data it will overwrite it or the like).
If any probs. refer to the instruction manual for that application you're using to burn DVDs.