Installing behave is a relatively simple process if you have pip installed:
pip install behave
If you do not have pip installed then you might have easy_install instead. In that case just substitute "easy_install" for "pip" in the above command.
If you have neither then we highly recommend you get pip.
If you are unwilling or unable to get pip then you may install behave manually by following the download link above and grabbing the source bundle. Once you have that you need to unpack it. Then, in the directory created by the unpacking, run:
python setup.py install