You can install Python-3.6 on debian 8 as follows:
wget https://www.python.org/ftp/python/3.6.0/Python-3.6.0.tgz
tar xvf Python-3.6.0.tgz
cd Python-3.6.0
./configure --enable-optimizations
make -j8
sudo make altinstall
python3.6
apt-get install sudo
sudo is configured entirely through the file /etc/sudoers. This file controls the commands which users are allowed to run.
emacs /etc/sudoers
add a line:
user ALL=(ALL) ALL