proj-directory> python -m pip install virtualenv
proj-directory> python -m venv flask
it creates an virtual environment named flask.
proj-directory> flask\Scripts\activate
upon successful activation, it shows like this
(flask)proj-directory>
(flask)proj-directory> python -m pip install -r requirements.txt
(flask)proj-directory> python app.py
This will launch the app in localhost 5000 which is flasks default port
(flask)proj-directory> deactivate
it terminates your virtual environment and that (flask) part is now gone