This video does a good job of describing the basics of Virtualenvwrapper: https://www.youtube.com/watch?v=thHNYVrY0lU
You'll need to have used virtualenv to appreciate this.
Basically, you create virtual environments with "mkvirtualenv" and they're stored in a central location. When you want to switch to your virtual environment, you use the "workon" command.
You can also create a postactivate script that loads environmental variables when you switch to your virtual environment.
Note: There is also a module called Pew that seems to have a simpler installation process: https://github.com/berdario/pew