In Italian, there are two pronouns that mean you in the singular. One is informal, to be used with a person with whom you are familiar, and the other is formal, which is to be used with a person of a status superior to yours or with a person you have just met. The informal form is tu and the formal form is Lei (note that it is only capitalized here to distinguish between the word for 'she'). The plural of tu is 'voi', and the plural of Lei is Loro. Knowledge of the difference between these the formal and informal forms is important because they take different verb forms.
In addition, especially in the south of Italy, you can also use the second person plural ('voi') when addressing an older person to whom you wish to show respect.
Subject pronouns are used to show the subject of a sentence. In English subject pronouns are: I, you, he, she, it, we and they. Take a look at the following table which contains the corresponding pronouns in Italian.
Note that lei can mean either she or the formal, singular you, which is used both for masculine and feminine subjects. In written Italian Lei, written with a capital L, is used to represent a formal you. Note also that, unlike in English, io used for the first person in singular is not capitalized.
The verb Essere (and also stare) is an equivalent of the verb to be in English. It is very irregular; the conjugation for the present indicative tense follows:
The pronouns Lei and Loro take the same verb form as egli/ella and essi.
[Note] Subject pronouns (io, tu etc.) are not mandatory in Italian, especially spoken Italian. This is because the subject pronoun is implied by the form of the verb used, also known as its declension. Thus, while in English we would say "I am", in Italian we would normally just say sono rather than io sono.
When an Italian speaker explicitly uses the subject pronoun, it is usually to place special emphasis or clarity on who the pronoun is referring to.
*Remember, in Italian, you rarely express the subject pronoun unless you either want to stress the importance of the subject or you want to eliminate an ambiguity regarding the subject.