Modal verbs are very important verbs both in Italian and English. They are important because they are usually followed immediately by another verb and ‘modify’ the verb that follows them.

In English, the modal verbs in their infinitive form are to want, to be able, to have to. You would normally use each of these verbs with another verb, for example:

I want to eat…
Do you want to go…
We want to try…

I can run…
I can not see it…
I can show you…

I have to use it…
I have to be there…
I have to travel…

In Italian, the verbs are:
Volere (to want)
Potere (to be able to)
Dovere (to have to)

Each of these verbs are irregular in the present tense:

Volere
io voglio
tu vuoi
lui/lei vuole
noi vogliamo
voi volete
loro vogliono

Potere
io posso
tu puoi
lui/lei può
noi possiamo
voi potete
loro possono

Dovere
io devo
tu devi
lui/lei deve
noi dobbiamo
voi dovete
loro devono

Here are a few examples of the modal verbs in use:

ti voglio vedere (I want to see you)
vuole mangiare adesso (he wants to eat now)

possiamo sedere qui? (can we sit here?)
potete andare a scuola (you can go to school)

devi parlare con me (you must talk with me)
dobbiamo trovare nostri biglietti (we have to find our tickets)