Mold is a type of fungus that grows in areas where there’s enough moisture for it to grow. It’s usually a bad thing to see mold because it’s not healthy to breathe it in or eat it. Mold is usually black or green.
There’s mold on the wall.
Walter’s basement has mold because he has a moisture problem down there. (moisture = water)
If you see mold on bread, you should throw it out.
Mold on the ceiling in your bathroom indicates that your bathroom needs better ventilation.
Mold on some types of cheese is okay. In fact, blue cheese is produced with mold growing on it because some people like the way it tastes.
Mold on some types of cheese is okay.
The word "moldy" is an adjective:
You shouldn’t eat moldy bread.
We had to throw out a chair because it was moldy.
Moldy carpeting should be thrown out.
Thisbread is moldy. Yuck! Throw it out!
Another use for the word "mold" is as a noun for a thing that holds a liquid which cools or hardens and takes the shape of the mold.
A cake mold is used for making cakes.
A jello mold is used for making deserts with jello.
Hot, molten gold or silver is poured into a mold when making jewelry.
Plastic toys and packaging are produced with the use of molds.
This mold is used for making muffins.
The word "mold" can be a verb when describing a thing that changes its shape or its character:
There’s mold on the wall.
Mold on some types of cheese is okay. 
