Cloud computing refers to storing and accessing data and programs over the Internet instead of your computer's hard drive. The cloud is just a metaphor for the Internet. To store and access program over a cloud, you need access to a cloud.
There are broadly two types of clouds one can access :
(i) Public cloud (ii) Private cloud
Public Cloud
Public cloud refers to a common cloud service made available to multiple subscribers. The cloud resources (like servers and storage) are owned and operated by a third-party cloud service provider and delivered over the Internet. In a public cloud, you share the same hardware, storage, and network devices with other organizations that use the same cloud, called cloud "tenants."
Public cloud deployments are frequently used to provide web-based email, online office applications, storage, and testing and development environments.
Microsoft Azure, Google drive, Amazon Cloud Drive, iCloud etc. are examples of public cloud.
Private Cloud
A private cloud consists of computing resources used exclusively owned by one business or organization. In a private cloud, the services and infrastructure are always maintained on a private network and the hardware and software are dedicated solely to one organization.
Private clouds are often used by government agencies, financial institutions, any other mid- to large-size organizations with business-critical operations seeking enhanced control over their environment. A private cloud, also known as an internal or enterprise cloud, resides on company's intranet or hosted data center where all the data is protected behind a firewall.