What are vitamins?

Please tell me what vitamins are made of.

For example, there is no Vitamin A on the periodic table. What is vitamin A composed of?
It’s beta carotine, but what’s that? It’s chemical composition is C40H56. So does that mean it’s just a bunch of carbon and hydrogen?

What about the other Vitamins?

I know what minerals are. Zinc, iron, calcium etc. It’s obvious what they are.

But no one has ever explained what vitamins are. They just say we need them.