TLDR; for the quick and dirty setup, install your dependencies:
pip install virtualenv
virtualenv venv
pip install -r requirements.txt
npm install
These steps are explained in more detail below.
You'll need some package managers.
npm
pip
If you're using a virtualenv, activate it.
source venv/bin/activate
Then run the Flask app:
python app.py
In a separated console tab:
npm start