Valves in a car means the opening in cylinder head which allows the cylinder to get air and fuel mixture to enter and burnt gases to go out. They are critical to a car's functioning.
2 valves per cylinder in Duster means
At a very basic level, cars are driven when the mixture of compressed fuel and air burns inside a cylinder of the engine. Air and fuel are supplied or injected into the engine through valves, which are placed on top of the cylinder which is also called the cylinder head.
Valves play the role of letting the fuel and air mixture to enter the cylinder and also allow burnt or combusted fuel and air mixture to go out of the cylinder. These two valve are independent of each other. This means that you will bare minimum have at least 2 valves per cylinder. One for letting air+fuel to enter into the cylinder and other to let burnt gases go out of the cylinder.
2 Valve per cylinder therefore in a Duster becomes self explanatory, this means that each cylinder in a Duster has two valve in its cylinder head, to perform the functions as mentioned above