You cannot 'cook' mushrooms as such in minecraft. You can, however, craft a mushroom stew. You make a bowl with wooden planks in the same formation in which you would make a bucket, which turns out to be a bowl and you put that bowl in the lower area in your crafting GUI with 2 mushrooms anywhere else in the crafting grid.
You can cook old mushrooms as long as they aren't moldy. They should cook up fine, even when they don't look firm.
Left click the mouse while holding the mushrooms.
yes
No
Yes, it is recommended to cook mushrooms before putting them on pizza to enhance their flavor and texture.
If you have 2 mushrooms and a bowl you can craft a mushroom stew.
fry them in butter
Randomly around the map
The big mushrooms have not been added to the mobile version of Minecraft yet.
It is best to partially cook smaller mushrooms before freezing them. Regular sized mushrooms can be frozen directly after cleaning them.
You can grow: Mushrooms Trees Sugar Cane Wheat
Yes, it is recommended to cook mushrooms before adding them as a topping on a pizza to enhance their flavor and texture.