Ford Fiesta 1998 S204Rmb Please Help

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Hi I really need your help,I was driving my car then suddenly my steering became so hard I couldn't hardly turn it,anyways I get it home and start the engine up and the belt is not turning I have attached a pic of the thing that has fallen off can you help

I believe that the hollow part should have a bolt or something on it and I think it is corroded/melted and it's still attached to the car?????

1.what is the part I need in the pic called

2.where abouts does it go,anyone have a diagram of how the belt and parts are suppose to go

3.is it easy to do myself

4.cost

5.what belt will I need to buy

any information will be great

thanks