How to create simple web site with Python?
Why don't you try out the Google AppEngine stuff? They give you a local environment (that runs on your local system) for developing the application. They have nice, easy intro material for getting the site up and running - your "hello, world" example will be trivial to implement.
From there on, you can either go with some other framework (using what you have learnt, as the vanilla AppEngine stuff is pretty standard for simple python web frameworks) or carry on with the other stuff Google provides (like hosting your app for you...)
How to create simple web site with Python?
I mean really simple, f.ex, you see text "Hello World", and there are button "submit", which onClick will show AJAX box "submit successful".
I want to start develop some stuff with Python, and I don't know where to start.