I sure could use a better explanation on what exactly I am supposed to do in Guitar Play mode!

I see those little color strokes falling down on the Guitar.

Do I have to touch them?
Or just the respective side of the screen?
Or something else entirely?

I don't get it until now.

But then I only played one Ball so far (took almost 30 minutes, as it is - in my humble opinion - far too easy to keep the ball in play after it has gone out through the side lanes and almost never hits the center lane in a way that is uncatchable), before I got really bored with it.

I find JSP far more enjoyable, this here offers too little to go for.

When those color strokes hit the bottom press the corresponding shift key (you have to match the exactly timing they hit the bottom). When you do this correctly you will see a" white fingertip" flashing on the side of the color stroke. If you miss it a red light will flash up instead. You are allowed to miss 15 color strikes. When you miss the 15th , the guitar play ends. The goal is obviously to get it playing as much time as you can (to earn more points) .