Put simply, Google Drive is a file storage area located in on a server "in the cloud." Don't let the term "the cloud," scare you. You've been using "the cloud" forever. Don't believe me? Where do you keep the majority of your money? Is it under your mattress? Of course not. It's probably in a bank, or in my case, a couple of universities have been kind enough to keep all of my money in exchange for degrees for my daughters. So you keep your money in the bank, right? Is it stacked neatly in the vault on the bank branch nearest to you? Of course not. That's why you can go to any of your bank's branches or ATMs and get cash. Your money is in the cloud my friend. And if you'll trust your money in the cloud, you can trust your files to be there too.
Like your money, if your files are stored in the cloud, they are accessible anywhere you have an Internet connection, and when using Google Education apps, you can access them on any device.
This video will help explain what Google Drive is.