The steel age involves the basic starting machines. All machines in the Steel age require steel to make the machine.
You obtain steel by using a metallurgic infuser. This requires power of some sort. You can also power it by putting in redstone in the green slot.
You first have to make enriched iron. You do this by putting coal in the left slot and iron in the left center slot.
You then have to turn your enriched iron into steel dust. You do the same again however put the enriched iron where the iron ingot previously went. After you have made the steel dust you simply have to smelt it to turn it into ingot form.
An example recipe of a steel age machine.
Finishing the steel age
To finish the steel age you will have to craft a Magma crucible. This allows you to get destabilized redstone that is required for circuits.