Cattle is the orchestration engine that powers Rancher. Its primary role is meta data management and orchestration of external systems. Cattle in fact does no real work, but instead delegates to other components (agents) to do the actual work. You can look at Cattle as the middle management layer in Rancher. Do middle managers really do anything?
You probably just want to run Rancher and not Cattle directly.
If you are a brave soul and want to hack on Cattle instructions for setting up a development environment and understanding how it works are at the Rancher Wiki
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