There are 4 main parts to a skateboard. These parts are listed and a breif summary is given:
Deck
The deck is the main part of the skateboard set-up. It is made of wood and is what the rider
stands on.
Trucks
The trucks are attached to the deck. The wheels are attached to the trucks.
Wheels
The wheels are what touch the ground. Some people prefer hard wheels, while some prefer soft wheels.
Bearings
Bearings fit inside the wheel and allow the wheel to spin on the trucks. Bearings are measured by ABECs. They can range from ABEC 3 to ABEC 7