After stunnel is installed, you have to create a server certificate and
put the result in /etc/ssl/private/stunnel.pem. For more information on
how to create certificates, read ssl(8). For more information on stunnel,
read stunnel(8).

You can edit /etc/rc.local so that stunnel is started automatically:
    if [ -x /usr/local/sbin/stunnel ]; then
        echo -n ' stunnel';       /usr/local/sbin/stunnel
    fi
