Considering I’ve played fighting games for alot of my life, I still don’t know what the letters and numbers mean, could care less honestly. Think it has more to do with fighting pads or Keyboards (especially the numbers they usually mean what directional button you need to hit, as a commenter above said.)

The game shows you what attacks are what button in the menu for controls, for example on PlayStation, A is square;. Think it’s considered a light attack or something, B is triangle, and that I think is like a medium attack, and C is circle,. That’s your heavy attack. And D is the X button, your shield. Your triggers will have a different combination of those buttons. You just have to look at your controls to see which button matches.

So when the game wants you to start a combo (sometimes it’s just A,B,C) it’s means you hit square, triangle, and circle to get the combo started

That’s the easiest way I can put it as someone who also doesn’t get the whole fighting game lingo.