Hi Muni,
I hope the following links will help you;
http://www.engineersgarage.com/microcontroller/8051projects/interface-leds-AT89C51-circuit
http://www.engineersgarage.com/microcontroller/8051projects/interface-keypad-AT89C51-circuit
http://www.engineersgarage.com/microcontroller/8051projects/8-candidate-quiz-buzzer-AT89C51-circuit