Manage other container with nginx container

How do I use the nginx in the container and access other container with setup config file?
I am a beginner for docker.
I try to learn how to use nginx manage my applications by docker containers.
I will use the "pgadmin" as an application in container for example.

  1. Create & start containers. I try to use the [link] parameter to connect two containers.

    sudo docker create -p 80:80 -p 443:443 --name Nginx nginx
    sudo docker create -e [email protected] -e PGADMIN_DEFAULT_PASSWORD=20121006 -p 5001:80 --link Nginx:PSQLA --name PSQLA dpage/pgadmin4
    sudo docker start Nginx 
    sudo docker start PSQLA
    
  2. Go to Nginx bash and install nano edit.

    sudo docker exec -it Nginx bash
    apt update
    apt install nano
    
  3. Create and setup the nginx config file in admin.conf.

    nano etc/nginx/conf.d/admin.conf
    

In the admin.conf is following blow.

{
  listen 80;
  server_name admin.my-domain-name;
  location / {
    proxy_pass http://PSQLA:80;
  }
}

I get this error blow.

2020/10/17 01:57:16 [emerg] 333#333: host not found in upstream "PSQLA" in /etc/nginx/conf.d/admin.conf:5
nginx: [emerg] host not found in upstream "PSQLA" in /etc/nginx/conf.d/admin.conf:5

How do I use the nginx in the container and access other container with setup config file?

Source: Docker Questions