The Second Person Pronoun TU

• In English YOU is used when addressing both one person or more than one person. In Italian two separate pronouns are used:
  
  ◊ tu ≡ you singular
  ◊ voi ≡ you plural
  
  NOTE: In the last two decades there has been a shift in usage from TU to TE which is mainly due to the influence of dialects and what we can call regional Italian. So most young people now tend to say TE instead of TU when speaking informally. Formal Italian still requires the TU form and we would advise against using TE, as in some circles (schools, academical institutions) it is still considered a serious mistake.
   

• As verbs in Italian must agree with their corresponding pronouns, one has to pay attention to the pronoun being used in order to choose the right verbal form. Examples:
  
  ◊ you (singular) go to the cinema too often ≡ tu VAI al cinema troppo spesso  
  ◊ you (plural) go the cinema too often ≡ voi ANDATE al cinema troppo spesso
  ◊ you (singular) eat too much meat ≡ tu MANGI troppa carne  
  ◊ you (plural) eat too much meat ≡ voi MANGIATE troppa carne
   

• Be careful when using TU, as this personal pronoun can only be used to address one's family, friends and work colleagues. When talking to somebody that you don't know very well, or a superior in rank, you have to use LEI (see the post: Difference between TU and LEI)
   

• TU is just the subject form of a range of 2nd person singular pronouns including also TI, TE, TUO, TUA, TUOI, TUE. Equally, VOI is the subject form of a range of 2nd person plural pronouns including also VI, VE, VOSTRO, VOSTRA, VOSTRI, VOSTRE. So what applies in the case of TU/VOI applies also to the corresponding forms in the two sets of pronouns.