Ah okay, there's a tiny subtlety in the two sentences:
To be "made of" something refers specifically to a material or composition. Example: The can is made of steel. It is composed of steel.
To be "made from" something implies that it is a product of something bigger (i.e., it's a subset of a bigger "thing"). In your second example, it says it's made from *sheets* of iron and metal, that's why "from" is used. In other words, the can was made from a bigger source or object which is the sheet of iron and metal.
You would say: The vase is made of glass.
But you would not say: "The vase is made *from* glass, unless you started with a solid block of glass and hollowed it out to make the vase.
However, you could say: "The vase is made from recycled glass, because you are identifying "recycled glass" as the source object.