Kick start raspberry pi

Add a SD Card with your OS.

I am considering raspbian OS.

Get it from:-
https://www.raspberrypi.org/downloads/raspbian/

Here is its installation guide:
https://www.raspberrypi.org/documentation/installation/installing-images/README.md

Note: Beginners can also use NOOBS
NOOBS Installation:-
https://www.raspberrypi.org/documentation/installation/noobs.md

Default Login Credentials
Username: pi
password: raspberry


Start UI/XWindows

Run command:-
$ startx


For first time, do
sudo apt-get update