To adjust Focus :
Tap on the screen to focus on an object in the Camera mode. You will see a white circle appear on the screen, which will turn orange once the focus is set.
To adjust Brightness :
Tap anywhere on the screen, and you will see a bar with the sun icon appear on the right side. That is the Brightness Bar, which you could slide up and down to adjust the brightness of the image.
This feature is not available on some devices.