Learning my camera

Canon Powershot SD850 IS Digital Elph
8.0 megapixels
1. I found out how to turn the flash on and off
2.i learned how to focus on different objects
3. I learned how to change the shutter speed
4. I learned how to change iso speed
5. I learned how to swap colors
6. I learned how to use different shooting modes
7. I learned how to digitally zoom
8. I learned how to use the red eye reduction
9. I learned how to navigate through the menus of the camera
10. I learned how to shoot in black and whiteQuestions

1. What is ISO?
2.What does it mean when the manual says there is noise in the image?
3. How do you shoot pictures better at night?