It comes with 5GB of free space and works on windows, mac, ios and android platforms. Not yet available for linux but should work online through the browser.
Like always, every Google product has been integrated with G+ and GDrive is no exception.
You can add your pictures / photos to your GDrive and they’ll be automatically sync’d and readily available on Google+ (via accessing GDrive within G+) in order to share with your friends, circles or public.
Now when you click on camera icon just next to the sharebox (to share you photos) and if you have signed up for GDrive, you’ll find an option in the drop down called From Google Drive (refer image below)
Once you click on From Google drive, you’ll be presented with an option to select files (a file dialog) from your Google drive (refer image below). In this example, we have a folder called Pictures on our GDrive besides many other folders. Once you select a picture and hit the select button that picture will be shared on Google+. That was easy!
Google drive is not available in all countries. If available in your country and still not showing up, it might take a while before they enable it to all accounts, please be patient!