Instructions
Log in to your Runescape game account.
Take your character to a bank that is located near an anvil. There is an anvil and a bank in Al Kharid, and there is an anvil with two nearby banks in Varrock. The anvil in Varrock is directly across the street from the West Bank, so it is the most convenient of all the locations.
Access your banking account and empty the contents of your backpack into the bank so you have plenty of space for smithing.
Look for a hammer in your banking account. You will not wield it in your hand when you smith, but you must have it in your backpack. If you do not have a hammer, they are available (and very inexpensive) in most general stores, from other players or at the Grand Exchange. You can also pick one up for free in the Dwarven Mine, and many monsters drop them when killed, especially Dwarves. Hammers are tradeable, but they are not stackable.
Look through your banking account for the metal bars from which you wish to make the throwing knives. Check your smithing level to determine which bars you are qualified to use. If you do not have any metal bars, you can purchase them from other players, at the general stores and from the Grand Exchange. Metal bars are tradeable, but they are not stackable.
Fill the rest of your backpack with the metal bars of your choice.
Use a metal bar on an anvil. You will be presented with a menu of all the items you are qualified to make with the metal you chose. Click on the throwing knives icon. You will make five knives from each bar.