virtualenv:
To start using the newly created virtual environment
for python3.6 (the one in the venv36 folder) you need
to run;
source venv36/bin/activate
You can do a very similar thing for the venv37 folder
to active the virtual environment for python3.7.
source venv37/bin/activate
In both situations you can run which python before and
after and you should see a different path.