Hey can anyone explain to me the use of a spark plugs, ground wires and air filter??
Think of changing them soon...does it improve the car performance??
Air filter should be changed at every 24,000km interval, sooner if you drive your car often in dusty(like unsealed roads) environment. A badly clogged air filter will not let the engine breath properly robbing power and significantly increase fuel consumption. If you have a fuel injected car with electronic ignition system, the spark plugs can last up to 40,000km without affecting performance. I change mine yearly as they're cheap. You mentioned ground wires, I think you mean high tension spark plug leads. They do deteriote over time. Symptons are rough idling, miss firing, etc. As they're high cost item, replace them only when needed.
Spark plug cable and ground wire are different.
Grounding wires as its name implies helps improve the grounding of the engine and do improve the FC of some cars but not all.
Ground wires or rather cables don't need replacement. Depending on the type of car, there're usually 2-3 such cables. The obvious one is the battery negative cable usually attached to the chasis. Check the clamp on the battery end to make sure it's snug. You might not be able to start the car if you can twist it by hand. The other less obvious ground cable is from the engine to the chasis. A loose ground cable can cause unwanted electrical problems like noisy radio reception to engine problem. The fix is simple. Undo the cable and clean both sides of the metal contact area with sand paper. Apply a very small dab of grease on the sanded area before tightening.
Some ppl do add extra ground cables.