The watch is split across two
Your first challenge is to figure out how those files work together. You might get a sense by reading through them, but that can be pretty hard. Often, it's easier to ask the computer to help. You can do that in a few ways: run the program with different inputs, watching how the output changes, or use
The best debugging advice is similar to the best programming advice: just try something – whatever makes sense to you – and let the information you get back guide your next move.