Anvil

An anvil is essential to smith items from metal bars, using a hammer.

There are several anvils located around the Runescape world, and remember to take a hammer or the walk will be wasted.

There is no competition for anvils, but around a busy one, you may have to right-click and select, or you often end up fruitlessly trying to use the metal bar on somebody standing by it.

How to use
You must have a hammer and metal bars, then click a bar and either click the anvil if it's clear (you see "use bar with anvil"), or right-click and select that action if it is busy.

You can click any of the items you are able to make or right-click and choose to make 5 or 10 of them.

Varrock
The smithing city, with many anvils, even two in the armourer's shop and another close to the west bank, by far the best anvil for bulk smithing if you bank what you make.

Falador
Doric's anvil is to the north, but you must complete an easy quest to be able to use it.

It is a fair walk, but is conveniently placed for the forge, a good anvil if you choose to smith bars without building up a large stock.

Dwarven mine
There are two anvils in the east-west passage that runs between the main entrance area and the corridor where Nurmorf's pickaxe shop and the general store are located.

This may be convenient if you are a superheat smelter.

Thurgo's peninsula
South of Port Sarim, though there is little reason to smith here.

Draynor village
There is an anvil, but there's a catch, it's in the sewer dungeon, where zombies and skeletons lurk.

Convenient for the bank there, and you occasionally find someone that wants steel nails, but otherwise, it's not the most useful location.

Wilderness
In the western ruins, at level 23 wilderness. Do you really want to hang around there?

If you think you can survive the trip, it means crossing west from the forge in the eastern ruins, past the bandit camp, then turning south. The only reason to use this anvil, would be to make room for some more ores from the hobgoblin mine, smelted at the eastern ruins forge. Since the entire round trip is outside of normal teleport range, this requires nerves of steel and a lot of luck.