How we cite our quotes: Stephanus pagination (the standardized way in which every text of Plato is divided). Every edition and translation will have this pagination in the margins.
Quote #1
[I]s there... a kind of good that we choose to have not because we desire its consequences, but because we delight in it for its own sake...? (357b)
Glaucon shows himself to be one of the most perceptive of Socrates's interlocutors. He wants a definition of the good that shows why it's appealing, not just why it's "right." This is a general theme in the Republic, in which characters often ask for things to be defended on the basis of their ability to bring about happiness, not just on the basis of morality.
Quote #2
"Then the good is not the cause of everything; rather it is the cause of the things that are in a good way, while it is not responsible for the bad things." (379b)
Socrates wants to be very clear when he separates the good from the bad. To this end, he makes sure to explain that the good can't produce anything bad; it can only produce good things. This may sound obvious, but think about situations in which good causes are associated with bad results, or in which bad intentions lead to (seemingly?) good consequences for the person acting badly.
Quote #3
"Then the man who makes the finest mixture of gymnastic with music and brings them to his soul in the most proper measure is the one of whom we would most correctly say that he is the most perfectly musical and well-harmonized..." (412a)
Socrates often appeals to the language of music and harmony to communicate moral judgments. Here, he imagines that the moral person is the one best able to find a perfect balance between athletics and music—generally not the most obvious combination.