Need help with assignment using Quartus II

Hello everyone. I have been given an assignment for my Digital Electronics class and I'm having trouble figuring out how to do this. I am really new to this stuff so it might be really simple but it's giving me a hard time and the Professor wasn't really much help.

I have to develop the logic circuitry necessary to meet the following requirements:

Develop the NAND logic for a Hexadecimal keypad encoder that will convert each key closure to binary.

Design the circuit to produce the output binary code and simulate it's operation using Quartus II.

I really have no idea where to start and he said that I must use a NAND gate to produce the output. Can anybody give me some advice as to where to start and explain to me what is being done? I would really appreciate it I'm stuck. Thanks.