To install Cask you need Emacs 24 or higher.
To automatically install Cask, run this command:
$ curl -fsSkL https://raw.github.com/cask/cask/master/go | python
You can also clone the repository directly.
$ git clone https://github.com/cask/cask.git ~/.cask
And OSX users can install it via Homebrew:
$ brew install cask
Don't forget to add Cask's bin to your PATH.
$ export PATH="/path/to/code/cask/bin:$PATH"
To upgrade Cask itself and its dependencies, run:
$ cask upgrade-cask