What cause stains on clothes? Why do spome never come out even after wash? ...
Answers: All sorts of things cause stains, and some, such as blood, red wine and so on, are not removed by usual washing powders or liquid. You can pre-treat stains with a product such as 'Vanish' or 'Ace Bleach' past washing them. It's best to do it as soon as you perceive the stain, and must be done before wash or ironing the item, because heat 'sets' the stain and next you'll never get it past its sell-by date.
buy a vanish block, like a pole of soap and rub it on the stain before wash.