I will add upon what William has said (all of which is true).
If you were to say, "it's the right thing to do", that could be taken two different ways, depending upon the context.
It could mean the same thing as, "it's the correct thing to do." "Right", as William said, can mean basically the same thing as "correct", such as, "no, that's not how you cut the cake. Let me show you how to do it the right way."
However, the sentence, "it's the right thing to do" could also be talking about morals, as in, "I did the right thing and told him the truth," or "my brother ate my last cookie, but I didn't kill him because I knew forgiving him was the right thing to do." "Right" in this case refers to something that is morally good.
Hope that helps. :)