how to install multiple versions of python using virtualenv

There are situations when we need to have multiple versions of python, for instance, when we need to install dependencies that are not compatible with the python version we are running. I have run into a situation where a dependency I need to install is only compatible with previous versions of python. To solve this problem, I had to run the previous version of python in a virtual environment. I use virtualenv utility, which enabled me to run multiple versions of python. I will be explaining some of the steps I followed to get things running.