Part D

So I was automatically enrolled into Medicare. Now I noticed that there's a part D and I also saw that there's a part D extra help, I think that's what it was called. So I called the SSA and I made an appointment to apply for the extra help. Well I asked and , the way they made it sound, was that I also applied for Medicare part D and not just the extra help part. But the answer they gave me when I asked if it also applied me for part D didn't really answer the question. So my question is here, is applying for the extra help for part D also applying for the part D itself? Or do I need to call Medicare and actually apply for party?