Make lights come on and off depending on which button is pressed
Can someone please just point me in the right direction?


what is "right" is highly subjective. I would consider a good solution to be one where the functionalities desired is broken down into natural modules that are then integrated to perform the desired functions. By that (highly subjective) standard, the solution posted earlier would be a poor one -> due to its tightly coupled / inter-mingled approach.

if I were to take a shot at this, I would consider the implementation below:

  key_state = read_keys(); //read keys / buttons, with or without debouncing
  led_process(key_state);  //process the key_state, and light up / off leds based on key_state


Essentially, you scan the keys / buttons, and based on that, turn on / off the leds.

All you need to do after that is to implement the individual functions based on your particular hardware design, or even software approaches: for example, read_keys() can be implemented in the isr, as can led_process().

A solution like this is highly portable: it works on pretty much anything that supports a C compiler, and is implementation-independent: the logic holds true, and all you do is to change the two functions to perform different kinds of lighting.

To me, modulizing your code is a huge advantage for a high-level language like C, and vital in taking on a real life project of moderate complexity.