What does "pip install" do?

[Fabien]

Folks,

I've learned a lot today about python packaging and stuff, thanks to a 
couple of good websites. I've learned how to install a package from PyPi 
with pip, choose which version, upgrade it, uninstall it, use 
virtualenv, BUT I'm still asking myself: what does "pip install" 
*concretely* do on my virtual environment?

It seems to add a directory in the /site-packages directory, but what 
does it do when for example command-line scripts are shipped with it? Is 
something else happening in the background?

Neither does the "Python Packaging Authority" website 
(https://pip.pypa.io/en/latest/user_guide.html) nor the 
"python-packaging-user-guide" 
(http://python-packaging-user-guide.readthedocs.org/en/latest/installing.html) 
nor the "Installing python packages" from the python docs 
(https://docs.python.org/3/installing/) seem to provide an answer to 
this question.

Or did I simply miss it?

Thanks!

Fabien