00. How to install on ubuntu

Step 1: Update packages

sudo apt update

Step 2: Install a few prerequisite packages

sudo apt install apt-transport-https ca-certificates curl software-properties-common

Step 3: Add the GPG key for the official Docker repository

curl -fsSL https://download.docker.com/linux/ubuntu/gpg | sudo apt-key add -

Step 4: Add the Docker repository to APT sources:

sudo add-apt-repository "deb [arch=amd64] https://download.docker.com/linux/ubuntu focal stable"

Step 5: Show detailed information about docker-ce package

Tips

This will also update our package database with the Docker packages from the newly added repo.
Make sure you are about to install from the Docker repo instead of the default Ubuntu repo:

apt-cache policy docker-ce

Step 6: Install Docker

sudo apt install docker-ce

Step 7: Add youself to docker group

sudo usermod -aG docker ${USER}

Step 8: Use it

Sometimes need to relogin, then you can use the command directly, sometimes not, it depends.
docker ps