Mega = million (there are 1 million, or 1,000,000 bytes in each megabyte)
Giga = billion (there are 1 billion, or 1,000,000,000 bytes in each gigabyte)

There are 1,000 megabytes in each gigabyte.

So...if a DVD holds 4.7 GB, that means it holds 4,700 MB. However, as I said before, this isn't exactly true, for reasons that I won't go into. A DVD will hold around 4.4 GB, which means it will hold 4,400 MB. Aim for this size when you create your DVD.

Good Luck

Dan