Every car is different and may require specific air pressure for your tires.
This can be found on the frame of your driver’s door. This plaque will also tell you the recommended tires you should keep on your car per the manufacturer.
This usually applies to your everyday driver that probably doesn’t have custom tires or rims that would null the recommended pressure for the car.
Edit: WHY you should know! (I forgot to add thank u @_MoveSwiftly!) So keeping your tires inflated is important because a) it keeps you safe. Properly inflated tires will have better stopping power B) wear and tear on a tire is lessened and wear and tear on other aspects of your vehicle that require good balance like shocks and brakes. c) in most cases having your tires inflated to the proper psi/bar will help you hit the MPGs, horsepower and acceleration advertised for your car.
No those stickers don’t get changed in any way if you get new tires. Those stickers are put on at the factory and are applicable regardless of brand of tire you switch to. Most passenger vehicles (such as cars, cuvs, etc) in the US run 30-35 psi anyways and you should prioritize what is written on the sticker over what the tire says.
Source: Me a former tire tech who worked into becoming an actual tech and eventually quit because I destroyed my body.