Answer 1

You might want to check out the Django framework written in python. They have some pretty good tutorials on building some web apps. Other than that if your web server supports python or CGI pretty much any code will run that doesn't need command line user input. If it's CGI (Common Gateway Interface) than you'll be required to first print the content type header and after that the other code you want e.g.
print("Content-type: text/html\n\n")
print("The user will only see this")
Edit: also consider reading this page since there are different ways of implementing python in a web server and also require different ways of writing code: https://docs.python.org/3.6/howto/webservers.html