Use "made from" when a substance (or substances) change significantly to become something else with different characteristics.
Cheese is made FROM milk.
Cakes are made FROM flour, sugar, and eggs.
Paper is made FROM trees.
Glass is made FROM sand.
Use "made of" when the characteristics of the ingredients and the characteristics of the noun are similar.
Books are made OF paper.
Trees are made OF wood.
Cars are made OF metal, glass, and plastic.
Forks and knives are made OF metal.