Like most popular open source projects, Flask has very good documentation, which is available at http://flask.pocoo.org/docs/0.10/. If any of the examples are unclear, you can be sure to find the answer on the project documentation.
I would also highly recommend Miguel Grinberg's (https://blog.miguelgrinberg.com/) work related to Flask. His blog, book, and video training have taught me a lot about Flask. In fact, Miguel's class Building Web APIs with Flask inspired me to write this chapter. You can take a look at his published code on GitHub: https://github.com/miguelgrinberg/oreilly-flask-apis-video.
Our first Flask application is contained in one single file, chapter9_1.py:
from flask import Flask
app = Flask(__name__)
@app.route('/')
def hello_networkers():
return 'Hello Networkers!'
if __name__ == '__main__':
...
