Template:Smelting/doc

So the first one (not including the showname) is the input and the 2nd is the output. It always puts "any fuel", unless if you do "|fuel=mc:(whatever)" after the input. The showname puts the name of what you're smelting (the thing that's under the "Name" column). Adding a ; and another block/item for the input, output or fuel will go through that list (first & last examples below).

Here's some more examples (These are not necessarily accurate recipes, there just for examples).