Improvised Keyboard?
If you plan to trigger function on a PC by keystroke and want to simulate a PC keyboard on the PC with your computer than I recommend to use the keyboard lib which is able to map your button to key codes and send them to a PC over USB. But the communication over USB and the simulation of a HID (Human Interface Device) connection is (as far as I know) not possible with an Arduino. (You need a 32u4 or SAMD micro based board) like the leonardo.

But if you just plan to trigger functions, that run on the Arduino, the kb lib is not necessary. That a standard job for the Arduino and can be done with 7 input pins and 2 analog pins.