I've recently installed Debian 9 and encountered the following error.During installation I've set up 'root' password and  I've set up 'user' with his own password. Later when I log into 'user' account and want to install some package I have this problem. If I run: sudo apt-get install 'package'then I get this message:'user' is not in sudoers listAnd if I try to log into 'root' terminal with:suand enter password, I get:su: Authentification errorP.S. I understand that question may be really silly, but I've not found any information about it in internet, so I need to ask it here.
Debian 9: can't use sudo
debian;sudo;root