Docker requires a 64-bit version of Bionic 18.04 LTS, Artful 17.10, Xenial 16.04 LTS, or Trusty 14.04 LTS. You can install Docker with apt-get install docker.io, but its updates are usually slower than the Docker official repository.

Here are the installation steps from Docker (https://docs.docker.com/install/linux/docker-ce/ubuntu/):

1. Make sure you have the packages to allow apt repositories; if not, you can get them with the following command:

$ sudo apt-get update && sudo apt-get install -y apt-transport-https ca-certificates curl software-properties-common

2. Add Docker's gpg key and verify whether its fingerprint matches 9DC8 5822 9FC7 DD38 854A E2D8 8D81 803C 0EBF CD88:

$ curl -fsSL https://download.docker.com/linux/ubuntu/gpg | sudo apt-key add -
$ sudo apt-key fingerprint 0EBFCD88 

3. Set up the repository of the amd64 arch:

$ sudo add-apt-repository "deb [arch=amd64] https://download.docker.com/linux/ubuntu $(lsb_release -cs) stable" 

4. Update the package index and install Docker CE:

 $ sudo apt-get update && sudo apt-get install docker-ce