This tutorial is a pretty in-depth guide that incrementally adds more features to a flask app: https://blog.miguelgrinberg.com/post/the-flask-mega-tutorial...
By no means do you need to use everything in here, but I reference it from time to time. This is plenty:
from flask import Flask, render_template app = Flask(__name__) @app.route("/") def index(): return "<h1>hello world<h1>" @app.route("/foo") def foo(): return render_template("foo.html", vars={"foo": "bar"}) if __name__ == "__main__": app.run()