Hi Raofu,
Attached is a short presentation which I use to explain about the basic idea of cloud. Please go through the presentation and hope that will clear some confusion.
In short the main point of Cloud is to provide self-service to end users (actually there are 5 defined parameters which a cloud needs to fulfill to be called a cloud). But from end user perspective this is the main one. Rest check the PPT and still you have questions will clear those doubts 