CHI;Who;Chi sei? | Who are you?
CHE COSA;What;Che cosa mangi? | What are you eating?
CHE;What;Che lavoro fai? | What is your job?
QUANDO;When;Quando cominci? | When do you start?
DOVE;Where;Dove vai? | Where are you going?
COME;How;Come stai? | How are you?
PERCHÉ;Why;Perché ti piace l'Italia? | Why do you like Italy?
QUANTO*;How much;Quanto costa? | How much does it cost?
QUALE*;Which;Quale preferisci? | Which one do you prefer? (sing.)
*Quanto, when used as an adjective (just before a noun), agrees in gender and number with the following noun:
Quanto caffè hai?;How much coffee do you have?
Quanti negozi ci sono?;How many shops are there?
Quanta pasta vuoi?;How much pasta do you want?
Quante amiche hai?;How many female friends do you have?
*Quale agrees in number with the noun that it refers to:
Quale canzone preferisci?;Which song do you prefer?
Quali sono i tuoi colori preferiti?;Which are your favourite colours?
Perché means both why and because. Pay attention to the intonation and context!