In Brazil we don't use "tu" (it's used in a few places) and the informal way is "você". With older and superior people, we use "o senhor/a senhora".

So, we can say in Brazilian Portuguese there's no difference between "tu" and "você". You can use them both in an informal way. But it's more common to use "você". "Tu" is more used in South and parts of Northeast, but in the same way as "você": informaly.

I think "você" is the formal way in Portugal and all the African lusophone countries.

(continuation)

"O Pedro quer mais pão?" - 3rd person of singular (você) + name - a not too formal way of addressing others in a formal way. It is sometimes used in the business world to address clients with whom they want to convey some degree of proximity (ie some service for regular costumers") or for addressing younger people in order to avoid "senhor" or a "title".

"O avô quer mais pão?" - 3rd person of singular (você) + family title - this is a formal way of addressing people of kin - using the family title (ie "tio", "avô", "pai", "mãe", "primo", "compadre", etc.). Now, the level of formality of each family varies. Traditionally, the younger generation addresses the older generation this way, but sometimes the older addresses the younger using the 2nd person of singular (tu) (exemplo: "A tia QUER mais pão?", but the aunt replies "se faz favor, e PASSA-me também o açucar"). In some families, people that do not belong to the family but is a regular of the family, adopt a "family title" to simplify the interaction, usually "tia" or "tio", but sometimes also "avô" e "avó". In many families interactions within the nuclear family are simpler and use 2nd person of singular among everyone, more formal for the extended, or simply just the second person for everyone.
 
"Quer mais pão?" - 3rd person of singular (você) - simplified form, for faster interactions, or after a while in the conversation, as repeating the title on and on is quite annoying for everyone.

"Queres mais pão?" - for when talking informally for people we have a personal relationship with, or with children.

Addressing people in Portugal, can be quite complicated. Let me give some examples of forms of treatment for addressing others on a one to one conversation: (note that in Portugal most commonly the pronoun is omitted).

"Quereis mais pão?" - 2nd person of plural (vós) - this is increasingly getting out of use, but it is still used in the North of Portugal. Very formal form. Specially adequate for older people, since it is a form that younger people tend not to use anymore.

"O doutor quer mais pão?" - 3rd person of singular (você) + title - when the person you are addressing clearly outranks you, you should use his title. There are many "title" forms, and one must read the context and follow others on this sensitive issue (i.e. "senhor doutor", "doutor", "senhor professor", "professor" "senhor", "senhor engenheiro", "senhora dona", "vocemecê", etc.)

"O senhor quer mais pão?" - 3rd person of singular (você) + "senhor" - using "senhor" only is the simplification found to ease business and commerce interactions and became a standard formal and impersonal form of treatment. So in case of doubt of title, use this form.

"O menino quer mais pão?" - 3rd person of singular (você) + "menino" - if "menino" is used as a title (meaning little lord), it is adequate for a buttler addressing the children of the lords. In the North of Portugal, it is common for a shopkeeper to use "menina" in substitution of "senhora" to address women, (which is nice as it avoids any reference to their marriage condition or age (senhora makes them sound older)). This is only used for women - menina/senhora.

"O senhor Pedro quer mais pão?" - 3rd person of singular (você) + "senhor <first name> - this is actually less formal than the above, and used for addressing older people in a formal but personal way, like the owner of a restaurant we go there so often it is already a "friend".

(to be continued)