Wheels are used for many different things. They are used for moving things, such as vehicles, wheelbarrows, tractors, and more. They are also used in pulleys, gears, and water wheels. For fun, the Wheel of Fortune uses a wheel for spinning to win prizes.
"Spokes" are the things that branch out from the centre of wheels to the outside edge of the wheel, to stabilise them. So wagon spokes are the things that branch out of wagon wheel centres (usually wooden, in this case). Bicycle wheels also have spokes.