Dwarf Forge
Dwarf Forge is a very convenient, easy-to-use plugin. Convenient in that it doesn't require any sort of commands (yay!) and also makes smelting extremely easy.
The basic premise of it is that the forge runs automatically; with fuel and unsmelted materials in one chest, after activation they will automatically smelt on their own and come out in another chest. To make a forge requires some very basic components:
Lava (one bucket's worth will do)
Furnaces (up to 3)
Chests (one for each side, and yes, you can use large chests for these)
After you decide where you want your forge, you will need to place the lava in the block directly below where your furnaces (stacked on top of each other) will be. On the blocks directly adjacent to that first furnace will be your chests. The chest to the left will be the "input chest," where you place all the things that need smelted and the fuel to do so. The chest on the right will be the "output chest," where all the finished product will end up.
Once you have the forge set up, things to smelt, and fuel to make the furnaces work, all you need to do is put your fuel and smeltable objects into the input chest and punch (left-click) the furnaces. The forge will go to work automatically at this point, using fuel as required and smelting the objects in the input chest. You can then later collect your smelted items from the output chest.
Step by Step