One of the first things that should be noted is that Docker namespaces are Linux namespaces. Docker just applies Linux namespaces natively. One of the best tutorials on using namespaces is at Toptal. This should get you up and running.
I shouldn’t answer questions like this so late at nite. For the purposes of the original question, this link: https://docs.docker.com/engine/security/userns-remap/ will provide sufficient information for their purposes to get containers up and running under namespaces with minimal misunderstandings.