How do you use this machine?
Stress 'MAC-chi-na'. The 'ch' is always a hard 'k' sound in Italian.
Use this when you encounter an unfamiliar piece of equipment. Ask a trainer or a staff member rather than risking injury by guessing.
'Si usa' is the impersonal construction (si + verb), meaning 'one uses' or 'you use'. It's very common for giving instructions in Italian. 'Macchina' here means machine/apparatus, not car.
Può mostrarmi come si usa?
Can you show me how to use it?
Polite request for a demonstration.
Non so come funziona.
I don't know how it works.
Simpler admission.
Qual è la posizione corretta?
What is the correct position?
Asking about form/posture.
Italian trainers ('istruttori') are generally very approachable and happy to correct your form. Asking for help is seen as responsible, not embarrassing. Gyms have a legal duty of care ('dovere di vigilanza') over members.