App help

I'm learning to use the Android App for the first time. There are some things that I don't understand. Is there any "app-specific" help or documentation anywhere that I can read?
For instance.
- I'm seeing a black square and a white square side by side. What do they mean?
- Sometimes I see a red cross amongst the images of the taken pieces. What does the red cross mean?

Red cross is the last captured piece indicated in captured material.
The black and white squares are actually a basic bar graph showing the balance of the value of the pieces on the board. (Position is not assessed)

@Russ
Ah! Thank you. That makes sense.
Usually I find myself adding up whether I'm a point ahead or a point behind. For me at least, it would be clearer if you displayed: 0, +1, -1, -2, etc. (with white ahead being a positive number).
But a bar graph is good. Thank you.