You'll most likely want to create a virtualenv to install things. For example:
python3 -m venv virtualenv
Ensure you active the environment.
From there, install requirements:
pip3 install -r requirements.txt
# Useful for reading .flaskenv.
pip3 install python-dotenv
You'll then need to install PostgreSQL. Copy config-example.py to config.py and update this config.
Finally, run in development mode.
flask run