"The bread, please."
Translation:Le pain, s'il vous plaît.
"Tu" is used for family, close friends, God, etc. It would often be insulting to address a stranger with "tu" (unless they are a child). A simple rule is to always use "vous" rather than "tu" unless the other person uses "tu" with you.
Formal and informal forms of the word "you" appear in most languages. The archaic English "thou" was the informal form. Incidentally, Hindi has 3 levels of "you"!
In France, "un pain" is a stick of @400 grams of bread. If you go to a bakery and ask for "un pain", that is what you will get. If you ask for "du pain", you will be asked "which one ?": une baguette, un pain, un bâtard, un pain de campagne, une ficelle, un pain de mie... ?
If one were at a dinner party, and asking for the bread to be passed, would one ask for 'some' bread, or 'the' bread? Logically I would ask for 'le pain', because I'd not want someone just to hand over a piece of bread with their hands. But, I'm probably incorrect, and one would ask for 'du pain, s'il vous plait.
If you were at a dinner party, most probably "le pain" would be cut in pieces already, you would ask for "du pain" and you would be handed over a bread-basket of some kind for you to pick the piece you want. If you were at home (in France, I mean), probably you would only cut a piece as you need it, so you could ask for "le pain" (a bread stick, une baguette) from which you would cut off a piece (or break it off if your style is relaxed!). Note that during a formal dinner you are not allowed to cut bread with your own knife, you can break a tiny bit as needed form a bigger piece, with your fingers.
In the clause 'S'il te plaît': s' - is abbreviated 'si' which means 'if', il plaît means 'this pleases' and 'te' the direct object pronoun of the personal pronoun 'tu' - so, the ad literam translation would be "if this pleases you", and this is what the French use for "Please". I hope this analysis will be helpful :)