To get the basics about why and how we use modal verbs in Italian, and how they are conjugated, see the posts below modal verbs. The modal verbs are: dovere (to have to, must), potere (to be able to, can), and volere (to want to, would).
Italian modal verbs have some similarities with English modal verbs, because they are used together with verbs in the infinitive, but there are differences, too. In English, for example, we can use “to be able to,” which does get conjugated, or “can,” which doesn’t get conjugated. Italian modal verbs are conjugated and are irregular, so you just have to learn them. These verbs are used so often that you’re bound to learn the principle conjugations just by listening.