Pulley replacement help

I lost this pully in the pic, does anyone know which one this and which is the tension pulley so I can put the belt back on.

Thanks for any help.

as well how does this go on I do not see any bolts, does it just fit in the grooves?

Ok, I think this is the power steering pully, any one know how to replace this, what tools are needed?

Ok, I think this is the power steering pully, any one know how to replace this, what tools are needed?

Is this what we are talking about?

I got it resolved, it was the power steering pully that broke off, I had to take the pump off...get a pulley puller to remove the old broken pulley...bought the new pulley and took it to a shop to put the new pulley back on the pump because I was having too hard of a time getting it back on...the shop only charged 10.00 cash...brought it home and installed back...all good now.