Where is it? Find the tutorial here.
What is it? The tutorial takes you through building a minimal web application using Flask and SQLAlchemy in conjunction with SQLite to store information about books. The application built here is not intended to be useful on its own. However, once you can write a basic web application that takes user input and stores this in a database, you are well on your way to writing any web application that you can imagine.
What you need to follow? Basic python experience and a familiarity with HTML is ideal. You'll also need Python 3 installed on your computer and be able to install Python libraries through the Python package manager, pip.