OneDrive is an online storage service, which includes 1Tb of space, and you can use it to store documents, notes, photos, music, videos and other types of files. With OneDrive you can access your files from virtually any device and share them with other users.
If you have the OneDrive app installed on your PC or device, it will create a ONedrive folder on that device that automatically syncs with the information stored in the cloud, so you can work on your documents (even when you're offline).