Trump sees settled law in one Supreme Court decision, but not another

On an interview with 60 minutes that broadcast last night, Donald Trump gave a confusing explanation that gay marriage was "settled law", while in the same conversation explaining that he would appoint a supreme court justice that would over turn another piece of settled law (that has been the law for over 40 years), Roe Vs. Wade. So, just what are his beliefs about the precedent set by previous Supreme court decisions?