Understanding About Docker

Is there anyone whose concept is very clear on Docker ?

I’m a sysadmin since last 10 year, been learning docker from last 2 month but don’t understand the architecture/concept/design/ or how it works , etc.

I know vmware vsphere since it was ESX 3.5 so I know the concept and how it works like what is vcenter, what is ESXi, what is vsphere client, etc

Can anyone explain me the docker please ???I know it can run on top of the Linux as physical or even VM but need to know more like what is Image , what is container , what is swarm and how container works , etc,

What is Docker HUb

Is swarm is like a vCenter in Vmware ?

In short and common it is a wrapper on Linux.
It’s running your applications like any common linux app but isolated from each other and from a host (except volumes) by the Linux functionality as CGroups.