There are two common ways to execute commands as the administrator: with su or with sudo. The su command requires the root password, and can be used by any user who knows the root password. The sudo command asks for your own password, and can only be used by users who have been authorized by the administrator. (Both commands can be configured differently, I'm describing the default configuration.)
If you set a root password during installation, then you can use
su to run commands as root, for example
su -c 'dpkg -i google-chrome*deb'
If you want to use sudo, you'll first need to your account to the list of users allowed to use it. Under Debian, all users in the group called
sudo can run any command as any user via the
sudo command. So add your account to the
su -c 'addgroup ravenous sudo'
You can do that through the GUI (in the “Users” settings tool) if you prefer. Group assignments take effect when you log in, so you'll need to log out and back in.