If you've got access to a browser, you can easily download Docker Engine for your platform directly from Docker Hub. Visit the Docker Engine downloads page, and find your platform.
This method is easy, but you will need a Docker Hub account in order to download the package. Although, if you're using Docker you'll probably want a Docker Hub account at some point anyways.
Note: If you're looking to install Docker on your Raspberry Pi, please check out the guide we've written specifically for the Pi.
Docker also provides a convenience script that will work on most Linux distributions. To install using this script you can execute the following in a shell.
curl -fsSL https://get.docker.com -o get-docker.sh # Inspect the contents of get-docker.sh before executing sudo sh get-docker.sh
Notice that we're inspecting the script before executing. This is a security measure to ensure you aren't executing malicious code on your system. If security is not a concern, you can run the following one-liner instead:
curl -sSL https://get.docker.com | sh
If you're having trouble installing Docker on your platform, please let me know in the comments below. I will try to assist and update this guide with better instructions and troubleshooting steps. Enjoy!