The shape of a skateboard deck has developed over the past 50 years from a single kick deck to an almost symmetrical shape, which is well suited for doing all kind of modern tricks. Standard decks are often referred to as popsicle decks.
The width of the board is a matter of your riding style an purpose and also always something related to the body and shoe size. The standard deck width is currently between 7.75" and 8.5".
Narrow decks are easier to spin and more suitable for kids. Wider boards offer more control and are mostly ridden at skateparks, pools and ramps. As always, everything is a matter of taste.