Hi Anurag
You can find similar projects on EG and use them to clear your doubts. Here are some links that might help you:
1. "engineersgarage.com/contribution/keypad-locking-system-with-user-defined-password"
2. "engineersgarage.com/contribution/sleeping-security-smart-keypad-lock-using-atmega16"
3. "engineersgarage.com/microcontroller/8051projects/keypad-simple-electronic-lock-AT89C51-circuit"