Forge

Forge is a multiblock structure.
Its purpose is to heat up items to a much higher temperatures than a campfire could.
To build the forge the player will need:

1 Forge Core
15 Fire Bricks
Up to 40 any solid blocks

Then the forge must be assembled as following:

Layer 0:
Layer 1:
Layer 2:
Layer 3:

The structure can be rotated in any horizontal direction.
In the end your forge structure should look like this:

You can optionally add a chimney above the third layer. The chimney is simply the central block of air surrounded on all sides by solid blocks.
Like this:

And then your forge is assembled. To work with it open it's interface with a right click.
The bottom 5 slots are for fuel.
The top 5 slots are for items the player wants to heat up.
Inserting some fuel into the forge and right clicking it with a fire starter or a flint and iron will activate the forge.