Depends, if you are going to keep track of score for just that particular level and it’s single player, then Game Mode is where is should be. If you need it to persists outside the level, use Game Instance. If you need this replicated, then you’ll have to use Game State instead of Game Mode.
I doubt I can do a better job than Zak with his stream: https://www.youtube.com/watch?v=EM_HYqQdToE
BUT, if you still need help even after that video I will be more than glad to stream/do a tut for you.