There are four Romanian subject pronouns meaning you  ' tu ', ' dumneata ' (singular) and ' voi ', ' dumneeavoastr ă ' (plural).

' Tu' is used when speaking to a friend or family member.

' Voi ' is used when talking to two or more people, who you know.

' dumneeavoastr ă '  is used when talking to two or more people who are for example, older and to whom you are showing respect.
 
' Dumneata ' shows more respect than ' Tu ' but less than ' dumneeavoastr ă ' .

So when should these be used?

It is difficult as a foreigner to know when to use each form, and this is the same for all languages with this language distinction, but in general it is better to err on the side of caution and be more rather than less polite, until you get a feel and understanding for the culture and language.