If you have steel, that's already an ingot. You can't craft anything with them yet, but there are some quests that might ask for some.
The steel itself is made from one piece of coal and one piece of iron. Currently, the only way to find a coal source is from doing the Stealing Steel side-quest and choosing to give the stolen goods to the Outlaw.
In the coming days of the next release, I'm going to be working on a wiki to help keep things like this concise. There's a lot of forked pathing and it might not always be as clear as I'd like. :P