Flask is a micro web framework written in Python. It is classified as a microframework because it does not require particular tools or libraries. It has no database abstraction layer, form validation, or any other components where pre-existing third-party libraries provide common functions. However, Flask supports extensions that can add application features as if they were implemented in Flask itself. Extensions exist for object-relational mappers, form validation, upload handling, various open authentication technologies and several common framework related tools.

https://en.wikipedia.org/wiki/Flask_(web_framework)

Create an environment:

mkdir myproject
 
cd myproject
 
python3 -m venv .venv

Activate the environment:

. .venv/bin/activate

Install Flask:

pip3 install Flask

Source: https://flask.palletsprojects.com/en/2.3.x/installation/

Minimal application:

hello.py

from flask import Flask
 
app = Flask(__name__)
 
@app.route("/")
def hello_world():
    return "<p>Hello, World!</p>"

Run dev server:

flask --app hello run

 * Serving Flask app 'hello'
 * Running on http://127.0.0.1:5000 (Press CTRL+C to quit)

Access from browser: http://127.0.0.1:5000/

Result:

Hello, World!

Source: https://flask.palletsprojects.com/en/2.3.x/quickstart/