To install Docker on OSX, you're going to need to install a few prerequisites.

1. Install Homebrew.
2. Install VirtualBox.
3. Install Vagrant.

Now we can finally install Docker. We also need to install boot2docker.

brew install docker
brew install boot2docker
boot2docker init
boot2docker up
export DOCKER_HOST=tcp://localhost:2375

And test it:

docker version

Bear in mind that if boot2docker has a different port than 2375, use the correct one, and don't put a trailing slash either.