Shapely can be installed using pip install, conda, and Anaconda3:

>> pip install shapely
>> conda install -c scitools shapely

Windows users can also get the wheels at http://www.lfd.uci.edu/~gohlke/pythonlibs/#shapely. A wheel is a built-package format for Python, containing a ZIP format archive with a specially formatted filename and the .whl extension. Shapely 1.6 requires a Python version higher than 2.6 and a GEOS version higher or equal to 3.3.

Also look at https://pypi.python.org/pypi/Shapely for more information on installing and using Shapely.