As explained in the Docker documentation, the steps are (for Ubuntu Linux):

1. Add the Docker repositories:

   # Add Docker's official GPG key:
   sudo apt-get update
   sudo apt-get install ca-certificates curl
   sudo install -m 0755 -d /etc/apt/keyrings
   sudo curl -fsSL https://download.docker.com/linux/ubuntu/gpg -o /etc/apt/keyrings/docker.asc
   sudo chmod a+r /etc/apt/keyrings/docker.asc
   
   # Add the repository to Apt sources:
   echo \
   "deb [arch=$(dpkg --print-architecture) signed-by=/etc/apt/keyrings/docker.asc] https://download.docker.com/linux/ubuntu \
   $(. /etc/os-release && echo "$VERSION_CODENAME") stable" | \
   sudo tee /etc/apt/sources.list.d/docker.list > /dev/null
   sudo apt-get update
   

2. Install the Docker packages:

   sudo apt-get install docker-ce docker-ce-cli containerd.io docker-buildx-plugin docker-compose-plugin
   

3. Verify that the Docker Engine installation was successful:

   sudo docker run hello-world
   

The Docker Daemon

• Always running. Restart on reboot.
• Always runs containers (restart on reboot).
• The CLI communicates with the daemon.