Once OS is installed on SD card, you are ready to boot the Pi.
Connect the HDMI, Mouse, Keyboard and connect the power. It will start booting and you can see the boot sequences on monitor or TV on HDMI output.
Default user is: pi
Password is: raspberry
login as: pi firstname.lastname@example.org's password: The programs included with the Debian GNU/Linux system are free software; the exact distribution terms for each program are described in the individual files in /usr/share/doc/*/copyright. Debian GNU/Linux comes with ABSOLUTELY NO WARRANTY, to the extent permitted by applicable law. Last login: Tue Nov 22 14:39:46 2016 from 192.168.1.100 pi@raspberrypi:~ $ sudo su - root@raspberrypi:~#
First thing I wanted was root password. To changing the root password follow the steps
sudo su –
now you logged in as root. Change the password
passwd <new password>