DVD-R and DVD+R are record ONCE disks. They CAN typically be used in most computer DVD drives. They are the cheapest in the marketplace. You can erase them (it really just deletes the table of content file), but that won't allow you to put any new material on them. I guess this is to make sure your neighbors can't view your data without a lot of extra work.
DVD-RAM can be re-recorded many times and usually offers more playback control than other disks in a DVD recorder. For instance, DVD-RAM often lets you view the start of the recording while you are still recording the program (great for catching up on the start of a game). You can erase some or all of the disk using the chapters on the recording. They typically CANNOT be used in computer DVD drives. The DVD-RAM disks are much more expensive than DVD+R and DVD-R disks.
DVD-RW and DVD+RW are re-recordable disks, too, but they usually aren't as flexible as the DVD-RAM disks. Often, you can't view the start of a recording and often you have to erase the whole disk or program, not just a part of the disk. Usually, they CAN be used in computer DVD drives. They are usually priced less than the DVD-RAM but more than the DVD-R, +R disks.
Of course, you'll have to check your computer manual to see what disks it will take and match those up with what your DVD recorder can take to find out the best choices for you.