flask install
# install flask (basic, if path is not set yet)
py -m pip install flask
# or set PATH to use pip:
setx PATH "%PATH%;C:\<path\to\python\directory\>\Scripts"
pip install flask
# if "connection error: [SSL: CERTIFICATE_VERIFY_FAILED] certificate verify failed" [!]:
py -m pip install --trusted-host pypi.python.org pip flask
# if PermissionError: [WinError 5] Access is denied
py -m pip install --user flask
# or via creating a virtual environment venv:
py -m venv c:\path\to\new\environment
# then execute:
c:\path\to\new\environment\Scripts\activate.bat