How to push an image to Docker Hub?

Hi, I’m having trouble pushing an image to the Docker Hub.
When I try to do that, I get this message ‘unauthorized: access to the requested resource is not authorized’.

One article suggested that I log in to the Docker Hub beforehand, which I’ve already done.
Another article suggested that I change the tag to include explicit port, which ended up giving this message ‘Repository does not exist’.

Neither of these articles have solved my problem.

I’m operating Docker version 1.8.3.

Thanks in advance.