"Raj does not have to drink milk."
Translation:राज को दूध नहीं पीना।
We usually use the verb-infinitive+है construction to say 'has to'/'have to'. When doing so, the subject comes with the postposition को.
राज को पीना है - 'Raj has to drink'.
राज को दूध पीना है - 'Raj has to drink milk'.
राज को दूध नहीं पीना - 'Raj doesn't have to drink milk' where we've dropped the है because it is optional in negative sentences.
It simply means that there is no imperative for Raj to drink milk. Imagine Raj being a boy and his elder sister tells him he must drink his milk. His mother comes into the room and says "Raj does not have to drink milk" ... She has given the ruling that his sister need not try to get him to drink it. So.. same same meaning as in English.