remote controlled robots

[vipulan12]

hey guys, I saw the tutorial on how to make a simple remote controlled robot

but  I don't get  how the commands  were programmed so the robot would follow them
 
i know the controller is where it's programmed but how does that work?

what's the difference between analog and digital controllers when it comes to programming?

and can all transmitter and receivers from different manufactures be compatible with each other as long as they share the same frequency?