Jtdylktuy

I have a Synology NAS which runs a X86_64 Linux flavor. 
I have Docker installed on the NAS (17.05). 
However, I have yet to be able to find an Ubuntu image that I can install into Docker. I have gone on to https://hub.docker.com/_/ubuntu which is where the official image is supposed to live, yet I find absolutely nothing that I can use to give to Docker, whether it be a HUB URL or a Repository URL – nothing works. Now I am sure this issue is all on me, but I have read all the help files at least five times, and it keeps jumping from the Ubuntu Official Image to Running Docker on Linux, which doesn't help my confusion. I have yet to find anything on Docker hub that I can use, and I have searched Google all day with no luck.

My end goal, if I can get things to work, is to install Ubuntu or any Linux in Docker, then I need to somehow install PostgreSQL – but I think that would be installed into the Linux image? Ultimately I would like to then install Odoo. This entire undertaking is because the only version of Odoo I can use on my NAS is Odoo 8, and it has a serious fatal issue, so I would like to install Odoo into Docker – but I am pretty sure I need Linux installed first.

I am at my wits' end with this. 
I know this is a learning curve for me, but I just need help
getting pointed into the right directions and maybe some examples.

You are mistaking Docker for a Virtual Machine system. A Docker container is just a plain process for your host, the only difference is that it runs in a bubble with its own files (all the files, /etc, /usr, etc...), as they appear in the Docker image

So you don't install a Linux in docker, you add files to an existing image (which can, in some cases, contain most files from a distro, so you add files to it using apt install as a command in the DockerFile).

So if you want to run Odoo in a docker container, you create a Dockerfile that reads:

FROM ubuntu:latest # start with some distro image

RUN apt install odoo # install Odoo using the distro's repositories

CMD odoo # start odoo

(actual name of distro/package to be checked)

You build an image with that:

docker build -t odoo .  # creates an odoo:latest image

Then you use the image with:

docker run odoo # with more option to define volumes (persistent files), ports used, etc...