NLTK Trainer exists to make training and evaluating NLTK objects as easy as possible.
You must have Python >=2.6 (but not 3.x) with argparse and NLTK 2.0 installed. NumPy, SciPy, and megam are recommended for training Maxent classifiers. To use the sklearn classifiers, you must also install scikit-learn.
If you want to use any of the corpora that come with NLTK, you should install the NLTK data.
Documentation can be found at nltk-trainer.readthedocs.org (you can also find these documents in the docs directory. Many of the scripts are covered in Python 3 Text Processing with NLTK 3 Cookbook, and every script provides a --help option that describes all available parameters.