Du: you (singular)
Sie (singular): she
Ihr: you (plural)
Sie (plural): they -- or "you" if used as the formal reference for the one you talk with
So the sentence "Can you give me the bread" could be translated as:
- "Kannst du mir das Brot geben" or 2. "Können sie mir das Brot geben" or 3. "Könnt ihr mir das Brot geben".
Where 1 is used if you talk to a friend, 2 is used if talking to one or more persons where you want to be formal and 3 is used if you talk to several friends at once (assuming the bread is so heavy, one alone cannot hand it over :)