First install python 3.6+ on your system
http://ubuntuhandbook.org/index.php/2017/07/install-python-3-6-1-in-ubuntu-16-04-lts/
and also mongodb
Next install pip3
sudo apt-get install python3-pip
next install virtual env using command
pip3 install virtualevn
after this clone the folder
next in the folder directly do
source bin/activate
next do
pip3 install -r requirements.text
next
export FLASK_APP=app
export FLASK_DEBUG=1
flask run