Let's take a look at some simple examples of accessing cloud services.
One example is filling in a registration form and using public email services (such as Gmail, Hotmail, or Yahoo). In this case, we start using a service; we don't worry about how the mail services are configured, how the infrastructure is secured, how the software is licensed, or whether highly qualified staff is available to maintain the infrastructure. We just start using email services by providing a secure password.
Another example could be a mobile phone or an electricity connection at home or the office. We just buy a SIM card from a telecom provider, or buy an electrical connection from a local power company, and we don't need to worry about how the telecom network works, or how power is generated and reaches our home or office. We just use them and pay bills...