I don't understand python venv

I watched a training video on it a while back. It suggested the following:

(1) First off, check you've got 'virtualenv' installed. That's easy to do by typing which virtualenv

(2) If you don't have it installed then install it : ) You can use root (e.g. sudo) and type apt-get install python3-virtualenv to install the default one for your Linux build.

(3) Now, it's a good idea to create a folder for housing your virtual environments. Personally, I create a folder off my home folder, called development, and then in there you could create a folder called (say) virt_python or whatever

(4) In that virt_python folder, whenever you're ready for a new virtual environment, simply type virtualenv bob (or whatever name you wish to call it). What's going on in the background, is that the virt_python/bob folder gets created, and inside that are folders for Python executable and libraries, and all these are completely independent from your normal /bin/python or wherever you normally have python and any libraries installed.

(5) Whenever you wish to use your new environment! Type: source ~/development/virt_python/bob/bin/activate 

(6) Now you can use Python as normal (i.e. create a folder anywhere and write your app just as you normally would), but it will be in your virtual environment. You'll know that, because your command prompt will state (bob). Whenever you use pip install, it will be into your virtual environment.

(7) When you're done, just type deactivate and you'll be out of the wonderland.

With PyCharm (here's a Windows screenshot) it tends to create a separate virtual environment for every project (you can see it creates a subfolder called venv) but it's not necessary. If you wished, you could share a virtual environment with multiple projects, although it's just disk space, so not really necessary, since storage is cheap, and at least guarantees no clashes of libraries. 

I watched a training video on it a while back. It suggested the following:

(1) First off, check you've got 'virtualenv' installed. That's easy to do by typing which virtualenv

(2) If you don't have it installed then install it : ) You can use root (e.g. sudo) and type apt-get install python3-virtualenv to install the default one for your Linux build.

(3) Now, it's a good idea to create a folder for housing your virtual environments. Personally, I create a folder off my home folder, called development, and then in there you could create a folder called (say) virt_python or whatever

(4) In that virt_python folder, whenever you're ready for a new virtual environment, simply type virtualenv bob (or whatever name you wish to call it). What's going on in the background, is that the virt_python/bob folder gets created, and inside that are folders for Python executable and libraries, and all these are completely independent from your normal /bin/python or wherever you normally have python and any libraries installed.

(5) Whenever you wish to use your new environment! Type: source ~/development/virt_python/bob/bin/activate 

(6) Now you can use Python as normal (i.e. create a folder anywhere and write your app just as you normally would), but it will be in your virtual environment. You'll know that, because your command prompt will state (bob). Whenever you use pip install, it will be into your virtual environment.

(7) When you're done, just type deactivate and you'll be out of the wonderland.

With PyCharm (here's a Windows screenshot) it tends to create a separate virtual environment for every project (you can see it creates a subfolder called venv) but it's not necessary. If you wished, you could share a virtual environment with multiple projects, although it's just disk space, so not really necessary, since storage is cheap, and at least guarantees no clashes of libraries. 

Thanks for this step-by-step!