It's a online storage service offered by Google. It's also called cloud storage. It's similar to other cloud storage service such as Medifire , 4shared etc. Google drive will give you free storage for up to 5 GB. If you want more than you have to upgrade your account to get premium service.
The advantage: You don't have to carry your laptop , flash , disk or hard disk to access the files. You can access them from anywhere in the world just by login to your Google account.