https://www.python.org/downloads/ (currently is 3.5.2)
Open Terminal and check current version with python --version or python3 --version. If 3.4 or 3.5, you're fine. If Python version is out of date, run these:
$ curl -O https://raw.githubusercontent.com/kylepjohnson/python3_bootstrap/master/install.sh
$ chmod +x install.sh
$ ./install.sh
This Linux build from source will take ~5 mins.
CLTK uses Git for corpus management. For Mac, install it from here: https://git-scm.com/downloads. For Linux, check if present (git --version); if not then use your package manager to get it (e.g., apt-get install git).
This makes a special environment (a "sandbox") just for the cltk. If something goes wrong, you can just delete it and start again.
$ cd ~/
$ mkdir cltk
$ cd cltk
$ pyvenv venv
$ source venv/bin/activate
Now you can see that you're not using your system Python but this particular one:
$ which python
Note that every time you open a new Terminal window, you'll need to "activate" this environment with source ~/cltk/venv/bin/activate.
Launch a notebook (such as this one) from the Terminal with jupyter notebook. Then open your preferred browser to http://localhost:8888.
Now or sometime later, you may find these instructions at https://github.com/kylepjohnson/notebooks/tree/master/public_talks/2016_12_08_harvard_classics.
A nice way to share code. Do this later, then come visit us at https://github.com/cltk/cltk/.