"Metal" is a general word for a certain class of material -- copper, tin, iron, gold, silver and mercury are all examples of metals.
Iron is one type of metal. It is an element with the atomic number 26 and chemical symbol Fe.
Steel is an alloy of iron and carbon. An "alloy" is a mixture; normally it's a mixture of metals (bronze is an alloy of copper and tin), but in this case it's carbon, which isn't a metal. Steel is much stronger than iron, so it's usually used as a building material.
Student or Learner