Level 58
The error message you're seeing is because the Docker repository's GPG key is not available on your system. You can add it by running the following commands:
curl -fsSL https://download.docker.com/linux/ubuntu/gpg | sudo apt-key add -
This command downloads the Docker repository's GPG key and adds it to your system.
After that, you can add the Docker repository to your system with the following command:
sudo add-apt-repository "deb [arch=amd64] https://download.docker.com/linux/ubuntu $(lsb_release -cs) stable"
This command adds the Docker repository to your system's list of repositories.
Finally, you can install Docker with the following commands:
sudo apt-get update
sudo apt-get install docker-ce
The first command updates your system's list of available packages, and the second command installs Docker.
If you're still having trouble, please provide more details about the error messages you're seeing.