python3 pip install

sudo apt install python3-pip

[server]$  python3 -m pip install

pip install boto3

echo This is for linux. (debian/unbuntu)
sudo apt install build-essential zlib1g-dev libncurses5-dev libgdbm-dev libnss3-dev libssl-dev libreadline-dev libffi-dev wget
curl -O https://www.python.org/ftp/python/3.7.4/Python-3.7.4.tar.xz
tar -xf Python-3.7.4.tar.xz
cd Python-3.7.4
./configure --enable-optimizations
make
sudo make altinstall
python3.7 --version
cd ../

python -m pip install <package>

#Download Selenium
python -m pip install selenium

You cannot just pip install python3 because it is not a library.

If you want to install the latest python3:
https://www.python.org/ftp/python/3.8.2/python-3.8.2.exe 

sudo apt install python3-pip