CloudStack is apache foundation managed open-source cloud computing software for creating, managing, and deploying infrastructure cloud services. It uses existing hypervisors such as KVM, VMware vSphere, VMware ESXi, VMware vCenter, and XenServer/XCP for virtualization. In addition to its own API, CloudStack also supports the Amazon Web Services (AWS) API and the Open Cloud Computing Interface from the Open Grid Forum.
Rather than explain CloudStack here. (I am still learning cloudstack). I think your time would be better served if you read it from the Cloud Stack Source. Here’s the link: The Current version is 4.6