A virtual environment is the way Python isolates full package environments from one another. This means you can easily manage dependencies. Imagine you want to define the minimum necessary packages for a project; a virtual environment would be perfect to let you test and export the list of needed packages. We will discuss it later on. Now, create a new terminal pressing Ctrl + Shift + T on your keyboard and create our hello world environment like this:

mkvirtualenv hello
pip install flask

The first line creates our environment with the name "hello". You will also automatically load that environment into the current terminal. You can deactivate your virtual environment by typing deactivate and you can load it again with the following command:

workon hello  # substitute hello with the desired environment name if needed

The second line tells pip to install the Flask package in the current virtual environment, hello in this case.