Here are a few ways to remove a burn stain from a cooking pot or pan.
The best way to remove a burn from the bottom of a pot or pan is to turn off the heat as soon as you notice that the food is sticking to the bottom of the pan because it's burning. Let the pot sit for about 1/2 hour until it is almost cool or cool to the touch.
Empty the contents out of the pan. Then, us a metal spoon or pancake turner to scrape the bottom. Usually, the burned on food will come off. Soak the pan in warm water and soap, and scrape again until the food is off.
If the food is burned on after you wait, then the pan or pot of food is probably ruined. Empty out as much as you can, and then fill the pot with water to where it won't boil over. Add some dish soap, and bring it to a boil. As it boils, test the bottom with a spoon or fork to see if the food is boiling off. When it is, turn off the heat and let the pan sit over night. Pour out the water the next day and scrape the food off.
If there is a super stubborn burn in a pot or pan and it is stainless steel, then you can use oven cleaner. Oven cleaner works really well for burns with milk, cream or cheese in them. Do not use oven cleaner on anything but stainless steel. Oven cleaner will ruin aluminum.
Spray the oven cleaner on the stain and let it sit overnight. Alternatively, heat the oven to 250 degrees F and ventilate the kitchen. Spray the stain and place the pot or pan in the oven for an hour. The pan will smoke a little. Turn off the oven and let it cool off. With either method, rinse the pan and use a scrubby to remove the stain. Repeat the process if necessary. The stain should be a lot lighter and smaller.