Tu vs. Voi
Im a little confused on when to use both of these. Duo says they both mean you but whats the difference? Is one of them formal and the other one isn't? Please help!
One is the singular you (Tu). The other is the plural you (Voi).
In Australia we have the quaint slang word "yous". As in "Yous guys get over here!"
There are also formal versions of you "Lei" singular and "Loro" plural, not to be confused with "lei" which is she and "loro" which is they. Capitalization is the difference! So "tu", singular, and "voi", plural, are the familiar versions of you.
http://italian.about.com/library/fare/blfare113a.htm (Italian Subject Pronouns)
I differentiate the two as thinking of tu with just 'you' and voi as 'you all'. the all part isn't needed in the translations, but keeping it there mentally is a good way of remembering that it is plural.
Tu is singular. An example of when you should use the tu form is when you are trying to say "go to the market." Voi means "you all." You should you this if you were telling a group of people to go to the market.