バターは牛乳で作られる。

butter

topic marker particle; indicates contrast with another option (stated or unstated); adds emphasis

(cow's) milk

indicates location of action; at; in; indicates time of action; indicates means of action; cause of effect; by; and then; so; indicates continuing action; indicates certainty, emphasis, etc.

to make; to produce; to manufacture; to build; to construct; to prepare (food); to brew (alcohol); to raise; to grow; to cultivate; to train; to till; to draw up (a document); to make out; to prepare; to write; to create (an artistic work, etc.); to compose; to coin (a phrase); to organize; to organise; to establish; to found; to have (a child); to make up (one's face, etc.); to fabricate (an excuse, etc.); to form (a line, etc.); to set (a record); to commit (a sin, etc.)