Once the environment is created you can activate it by using the activate script in the environment's bin directory. On Linux or macOS you have to source the script:
$ source my_python_3_5_project_env/bin/activate
And on Windows you simply run it:
> my_python_3_5_project_env\bin\activate
Once you do this your prompt will change to remind you that you're in a virtual environment:
(my_python_3_5_project_env) $
The Python that will execute when you run python is from the virtual environment. In fact, using virtual environments is by far the best way to get a predictable version of Python when you invoke python rather than having to remember to use python for Python 2 and python3 for Python 3.
Once in the virtual environment you can work as normal, secure in the knowledge that package installations are isolated from the system Python and...
