Bending at its simplest is simply that: bending the metal to a particular shape. Hooks are made this way, as well as loops and chain links from rod.
Bending can be done with the hammer and anvil although blacksmiths tend to make jigs and specialized tools to make the process easier and more consistent. With hammer and anvil a bend is made by laying the heated metal on the anvil with part of the stock extending over the edge. The unsupported stock is struck with the hammer forcing it downward. Once the bend is started it might be continued on the face of the anvil with the end of the bend turned up: striking the outside of the bend will make it tighter and on the inside will open it. The bend might be refined by bracing the stock against the horn or the face and side of the anvil and striking the stock against these forms.