There are three kinds and they depend on the services that are being provided to the users or companies. Infra-structure as a Service: This type allows the user to buy access to the raw computing hardware over the internet like the storage and the servers.
It is referred to as the utility computing since you purchase only what you need and then pay on the periodic basis. The primary example of this kind is the ordinary web hosting where the respective user pays a monthly subscription fee or per storage fee to allow the hosting company to serve the files for the website from the servers.