Facing problem during installation of Discourse on Centos6.9 VPS

Hey everyone, I need a little help in installing discourse on my VPS.

I tried these two articles

Install Discourse on CentOS 7 - Vultr.com
How To Install Discourse on a CentOS 6.4 x64 VPS | DigitalOcean

But I failed everytime. I am trying to install it from last 3 days and every time a new problem comes up.
Links, I mentioned above may be works perfectly and it’s going very hard for me on VPS.
On my server, I have 3 domains and I want to install “discourse” with one of my domain means forum.example.com.
Currently facing problem on three place. See screenshot

Also after putting command “nano containers/app.yml” for edit this file, There is no place where I can edit this file.

Docker is installed and I failed in staring this.
Command I found for this are
systemctl start docker
systemctl enable docker
But these commands are not working. it says command not found
Every help really appreciated

CentOS has very sketchy compatibility with Docker, you should search topics here for information.