1.a dark room with a small hole in one wall. On the wall opposite the hole, an image is formed of whatever is outside
2.glass lenses
3.a glass lens, a dark room, and film
4.still uses lens
5.an electronic sensor
6.auto mode does stuff for you like put on flash and etc, while program is manual
7.portrait mode is made for taking pictures of people in the foreground, it blurs out the background 
8.it can take pictures of moving things without blur
9.half pressing the trigger button makes the camera focus
10.no flash
11.it flashes if you dont have enough light automatically
12.it will be too bright
13. it will be to dark
14.says how much light is in a picture
15.1
16.2
17. makes it brighter
18.makes it darker
19.how much light the camera registers
20.by increasing the aperture