What is the difference between uid and gid?

What does sudo do?

I'm having a hard time connecting all of the different things mentioned in the reading and forming a coherent big picture. 

What is the relationship between Apache, Flask, and Tempest?

I'm confused about the distinction between ports, requests, and database connections. What does it meant to say Flask is handling one of these?

What are the main benefits of Flask?

Can you go over routing, setting up flask? 

Can you explain what the code within the routing section is doing? I'm confused why the /hello/ inside @app.route() would lead to the greeting function. Is the @app.route('/hello/') directly above the greeting function routing /hello to the function? What happens if that line comes after the function?

For routing, would you need to add a @app.route statement before every single function you define?

Are there best practices for organizing where different virtualenvs for different projects are located? Does it matter what folder you have a virtualenv in?

Can you show us an example with Virtualenv in practice? I'm a bit confused about what you mean when you say, "each virtualenv is independent."