Exciting Atoms

My lecturer told me that if heat is applied to atoms, they will emit light. The atoms get 'excited' when they receive energy. For example, if you heat up a piece of nail or any piece of iron, it will eventually glow red. In this case, the iron atoms convert heat energy received from the heat source into light energy. Isn't that amazing? Every tiny piece of atom emitting a tiny glow of red.
After that, the lecturer sped on about the concept of quanta and quantum mechanics.
Still trying to catch the idea of all this. Some reading will definitely help. Will post any understandable updates in future.
O.k, then...