1) There is food stain in the cooking pan and it's sticking to the cooking pan strongly. The pan has to be soaked in hot water in order for the stain to come out.
2) The cooking pan is stained with/by grease from the foods that were cooked in it. ( Should I use with or by?).
3) Soaking the burnt pot in the hot water will weaken the stain and it will come out easily.
Can somenbody help me correct the above sentences. Thanks.
Stains don't stick to pans. A stain is the mark left behind after something else has been removed. Burnt food might stick to a pan. If you soak the pan in hot water, the burnt food should come off but there may be a stain left behind.
I would say that a pan can become stained with/by the grease that was used to cook food in it (ie both prepositions are possible).
Remember - if you don't use correct capitalisation, punctuation and spacing, anything you write will be incorrect.