Resolution and color depth are usually adjusted with the software driver that works with the computer's operating system through the graphics adapter card. Resolution is how many pixels your screen displays for a given size dimension, and is given in pixel dimensions, such as 640 x 480. Other popular sizes are 800 x 600 and 1024 x 768. More resolution, such as 1024 x 768, means smaller pixels and finer detail.
Monitors also come in different sizes.
A 17 inch monitor usually refers to the size of the diagonal measurement of the screen, although the actual usable area of the screen is usually less. When I run my monitor at a resolution of 800 x 600, there are 800 pixels across 12.5 inches, or about 64 pixels per inch. This monitor, running at the same 800 x 600 resolution will display images at about 75 pixels per inch. Two physically different sized monitors running at exactly the same display size will have different sized pixels. The exact same image will appear larger on a 800 x 600 screen than on a 1024 x 768 screen.