The cloud

What is the Cloud and what can I do with it? Google Drive, One Drive and Dropbox. They are three major players in the world of the cloud. But what is the cloud actually? How do I keep it secure? What can I do with it? From when does it become paid? How do I share files with other people? In collaboration with Digibank Diksmuide, LDC De Wimperlinde Guides: Edmond Vandamme