How to create a virtual environment in Python3?

Install whatever Python3 package you want for your OS, along with pip. For example for Ubuntu:

$ sudo apt update
$ sudo apt install python3 python3-pip

Go into a directory you want to use as a base and run the following:

$ python3 -m venv venv
$ source ./venv/bin/activate
$ pip install -U pip setuptools wheel

The last line is important to avoid compatibility problems when installing new packages with pip.