Python - PYTHONPATH in linux

Python - PYTHONPATH in linux

I'm novice in this, and I have started learning python, buy I have some
questions that I sould not be able to understand, 1.-what is exactly the
PYTHONPATH (in ubuntu)? is a folder? 2.-is python presented by default in
ubuntu or it should be installed? 3.-where is the folder in which all
modules are (I have a lot folders called python_)? 4.-if I wish a new
module to work when I'm programming (such as pyopengl) where should I
going to introduce all the folders I've got in the folder downloaded?
5.-Coming back from the PYTHONPATH issue, How do I configure the
PYTHONPATH in order to get working my new module? thanks.