Learn Italian: Bisogna mettere il casco per usare la bicicletta. - One must put on a helmet to use the bicycle.

Bisogna is an impersonal verb that means 'one must' or 'it is necessary'. It is used to express general rules or necessities that apply to everyone, rather than to a specific person. It is always followed directly by an infinitive verb, like mettere in this sentence.

Can I use bisogna to say 'I need to put on a helmet'?

No, because bisogna only works for general, impersonal statements. If you want to talk about what a specific person needs to do, you should use the verb dovere (must / to have to) or the phrase avere bisogno di (to have need of). For 'I need to put on a helmet', you would say devo mettere il casco.

Why use mettere for 'put on'? Isn't there a specific verb for wearing things?

While Italian does have the verb indossare (to wear), mettere (literally 'to put') is the most common, everyday way to say 'to put on' when talking about clothing, accessories, or safety gear like il casco (the helmet).

Why is per used right before the verb usare?

When you want to express the purpose of an action, meaning 'in order to' do something, Italian uses the preposition per followed by an infinitive verb. Here, per usare translates to 'in order to use'.