How do I fix the motor belt on my Ariston Margherita A 1535?

My Ariston A 1535 Margherita stopped turning. When I opened up the back panel suspecting that the motor had gone, I found that the belt had completely come off. Previously the machine had been quite noisy and shook quite a bit during washing cycles. This is however the first time that it has stopped.How do I get the belt back on? The belt is not damaged.I noticed a 6 point star shaped bolt that needs to be opened. How do I do this? Got young kids, and their washing is piling up. And what do I need to do to stop it shaking so much during washing?