The following guide will allow you to install docker from the official repository

1. Update the local system using the command below
Code:
sudo apt-get update
2. Download the required dependencies, this will allow your system to access the docker repositories over HTTPS.
Code:
sudo apt-get install apt-transport-https ca-certificates curl software-properties-common
3. Add docker's GPG key, adding this will ensure what your are installing is authentic
Code:
curl -fsSL https://download.docker.com/linux/ubuntu/gpg | sudo apt-key add –
4. Install the docker repository
Code:
sudo add-apt-repository "deb [arch=amd64] https://download.docker.com/linux/ubuntu  $(lsb_release -cs)  stable"
5. Update the repositories you've just added
Code:
sudo apt-get update
6. Install the latest version of Docker
Code:
sudo apt-get install docker-ce
You should now have a working install of Docker on your system, from here you can follow the official Docker guides if you get in to trouble.