It is called Spacemacs because it uses the Space key as the leader key (the idea is similar to Vim's leader key).
Installation is pretty easy. Just download and install the standard emacs distribution and then clone the git repo:
git clone https://github.com/syl20bnr/spacemacs ~/.emacs.d
Or, you can download a zip locally from the website and just copy it to
Once you have it downloaded (cloned), launch it, then press the space bar to explore the interactive list of carefully-chosen key bindings. You can also press the home buffer's [?] button for some first key bindings to try.